Standard inter-war defense against destroyers was provided by the 5"/51 cal Mark 7, which fired projectile at an initial velocity of about 3,100 ft/sec. The nominal range of this gun was c. 20,100 yards at 45° elevation, but casemates typically limited the a elevation to about 20°, so the effective maximum was only about 16,500 yards instead.39 Long Range Battle Practice for the secondary or "broadside" battery typically divided the guns into a three or four-gun forward group and a two-gun after group. A typical practice would see the forward group open fire against a simulated torpedo attack by destroyers, after which the battleships would turn 60° away, presumably to avoid incoming torpedoes, and the after group would complete the practice. Ranges were usually about 10,000 yards for the forward group and 8,000 yards for the after group. Targets - often series 40 target sleds - were towed at about 20-24 knots, closing from about 70° off the bow.40
Although some battleships experimented with rapid continuous fire, with each crew firing as fast as it could load, this made spotting difficult and the general procedure was attempt to fire full salvos, synchronizing the various gun crews by means of buzzers. "Missing a buzzer" was considered a capital offense, as the crew would then have to wait for the next buzzer in order to shoot. Although the number of Hits Per Gun Per Minute continued to increase year by year, few officers were satisfied with secondary battery performance.41 In 1922, Lt. Cdr. F.J. Cromerford aboard Nevada would characterize the battery as ". . . decidedly inefficient." "In most cases the salvos are very well bunched," he wrote, ". . . but the patterns are not placed right, so hits are few. The service of the gun is [usually] excellent, the director and operators and pointers are on, and the rate of fire is good, so the trouble must be in the control."42 Although the battery could be very effective against a single ship, stopping a group of destroyers approaching in formation would be much more difficult. A single 30 knot destroyer, for example, could close from c. 16,000 yards to 10,000 yards (reasonable torpedo range) in about 7 minutes. Assuming six guns could engage, 0.35 hits per gun per minute - the fleet average - would yield fourteen hits, more than enough to disable it. Distributing the same fire among a half dozen destroyers in formation, which would require firing a barrage, would be much less effective. Assuming a barrage to be 30% as efficient as aimed fire, and dividing the total number of hits equally amongst six incoming ships would yield less than one hit per ship. True, the concentrated fire of four or five battleships might improve the situation somewhat, but not as much as one might think. Coordinating and spotting small caliber concentration fire was difficult at best, and would be, in most cases, well-nigh impossible.
C.T. Joy, in a 1929 lecture "Some Notes on 5-Inch, 51 Caliber Gunnery" gave some reasons why secondary battery fire control was so poor. These included a lesser number of men assigned to the task (13 as opposed to 60 for main battery), lack of experience, outdated equipment, the small size of 5-inch splashes (which made spotting difficult), and the relatively high rate of fire (7-10 seconds between salvos as opposed to 30-50 seconds for main battery shoots).43 Fortunately, between 4,000 and 11,000 yards, the new 5"/38 caliber gun, which was mounted on the pre-treaty battleships only after Pearl Harbor, was significantly better than the 5"/51 caliber gun it replaced. But it was primarily used against aircraft.
The change from a mixed battery of 5"/51 and 5"/25 guns to a single group of 5"/38s greatly simplified the fire control problem. For the first time, the battleships could fire their secondary batteries in true director control. Previous control of the 5"/51s had been, by comparison, relatively rudimentary. Fully enclosed gunhouses meant that internal lighting could be enhanced, which greatly improved efficiency, especially at night. The newer gun was much more effective under 12,000 yards and at least equally effective outside that range. The high-velocity low-trajectory 5"/51 was ballistically the superior weapon against surface targets and the increase in effectiveness was obviously due to better fire control.
Further, the 5"/38, having been introduced into the fleet some years earlier in destroyers, had been more or less completely de-bugged before it reached the battleships.44 And it was remarkably accurate. Unlike the main batteries, which employed delay coils to delay the center gun about 0.060 seconds, the 5"/38 twin mount fired both guns simultaneously. BuOrd found that installing delay coils decreased the 2-gun range pattern from 100 yards to 92 yards at 11,700 yards but, because firing one gun after the other rotated the mount, this was accompanied by an equivalent increase in the deflection pattern. 10 round patterns, representing a battleship broadside, tended to average about 175 yards at 10,000 yards and 335 yards at 12,000. By way of comparison, the six-gun secondary battery pattern size for West Virginia was 643 yards at 14,212 in 1925; 329 yards at 10,258 in 1929.
Writers fairly commonly ascribe the Navy's early defeats in the Solomons to neglected night training, but in fact, Night Battle Practices for main batteries, secondary batteries, or both, were fired almost every year. Several variants were available. Night Battle Practice "A" - fired against series 60 or pyramid sleds - was designed to test the ability of the secondary battery to repel surprise destroyer attacks at night. Night Battle Practice "B" was similar, but was conducted in conjunction with actual destroyers, who were simultaneously testing their ability to deliver night torpedo attacks. To make the practice even more difficult, the Officer Scheduling the Practice (OSP) was provided a sealed envelope which would authorize him to impose one of the following casualties part way through the exercise:
a) Controlling director out for two to five salvo interval.
b) Searchlight train and elevation indicators out for 20-30 seconds.
c) Star shell (illumination) gun out of action.
d) All battle telephones out for one to four salvos.
e) Controlling spotter out of commission for remainder of practice.
f) Any other casualty which will require a shift of control.
Night Battle Practice
"C" was designed to exercise both main and secondary batteries simultaneously.
The plan for NBP "C," taken from the Orders For Gunnery exercises, 1940,
foreshadowing the type of actions the Navy would soon be fighting off Guadalcanal,
reads:
"2T2a. Tactical Situation.
A division of battleships, operating as a detached wing, is proceeding at moderate speed during the night to rejoin own forces at daylight. Detachment is very lightly screened. Enemy surface forces are known to be in the area. A screening vessel encounters three enemy battleships on reverse heading and discloses their presence to the detached wing commander who takes them under fire with main battery. Shortly alter the main batteries open fire, enemy destroyers making an attack on the unengaged side are disclosed by another screening vessel, and secondary batteries take them under fire."
Target courses and speeds
were determined by successive rolls of a die. Night Battle Practices
imposed their own artificialities, of course. Illumination of the
towing ship, for example, was often necessary to prevent collisions or
confusion with the target. If unlighted, tugs would shine a search
light vertically, and wave it wildly in order to call off any dangerous
incoming fire.
Some ships employed searchlights to spot fire, while others used starshells instead. Searchlights were usually preferred to begin with, starshells could not be employed at ranges under three or four thousand yards whereas searchlights could commonly reach six or seven thousand.45 Because searchlights illuminated the area in front of the target, as opposed to starshell which left this area in relative darkness, spotting with searchlights tended to be easier and returned many more hits - usually about twice as many - as starshells did. Searchlights also allowed a much higher rate of fire, and some gunnery officers believed that a well placed searchlight beam might serve to blind enemy gunners as well.46 Lights did of course reveal the position of the firing ship, but the Navy hoped it could avoid the problem by placing them on smaller "screening" vessels which could illuminate the enemy from positions outside the battle line.47
Still, the effective application of searchlights was anything but fool-proof. (Pre-war, one officer facetiously remarked that they would be best employed for searching for survivors.) In haze, spray, smoke, or fog, back-scatter could cause sufficient flare to completely obscure the target, so a salvo of "shorts" landing near the firing ship might actually render the searchlights worse than useless. In concentration fire it was often impossible to tell exactly who was illuminating what. In the absence of reliable director control - i.e., anytime prior to World War II, when radar supplanted searchlights in any case - the lights were difficult to aim in either range or deflection.48 Own-ship gunfire often blinded or stunned the searchlight crews, and flue gases damaged the reflectors. Their previously mentioned tendency to emphasize shorts rather than overs sometimes caused spotters to put subsequent salvos over the target. And they were hard to maintain.49
In 1930-31, a typical year, the battleships fired Night Battle Practice B, for broadside guns. The practice - clearly anticipating Savo - was deliberately designed to determine what ammunition, if any, should be preloaded in the secondary battery in order to meet an unexpected night attack. The atmosphere was very clear, and the visibility was excellent. The mean range to target was about 5,000 yards, slightly lower than average.50 It was expected that ships might get their first effective shots off within 30 seconds, but no ship attained this standard. Because of this failure - 44 seconds being the average time to first effective salvo - further practices were scheduled to determine whether or not it might be better to turn on searchlights while the first salvos of starshells were still in flight. The average salvo interval was about 10 seconds, but performance among the various ships in the battle line varied markedly; Colorado's six-gun average interval of 5.9 seconds was lowest, while tardy Tennessee took almost twice that long. Everybody got some shots on target, although the hit percentage was rather unpredictable, ranging from Texas' 6.6% to California's 40.5%.
Some problems recurred in
both daylight and darkness. In the 1930-31 practice, for example,
Tennessee
placed the starshell gun under control of director No.3, and the rest of
the battery under control of director No.1. In the confusion of the
exercise, the two directors locked onto different targets, which pretty
much ruined her performance and undoubtedly generated a good deal of colorful
language from her crew. Such confusion was hardly uncommon, and even
in daylight practices it seems that at least one ship in every exercise
made the mistake of placing her directors on one target while her rangefinders
futilely tracked another. Similar problems are still encountered
today.
Early anti-aircraft exercises were fired against kites towed by destroyers or tugs. The speed of the target was thus relatively low, even in comparison with the relatively stodgy aircraft performance of the day. Even then maximum ship speed was rarely used; towing ships were actually cautioned against towing too quickly, as this might bring the kite line nearly vertical and place the target directly above. Sometimes tethered or free-floating helium (meteorological) balloons were used although the board appointed to review the use of these targets in 1921 cogently noted that they ". . . make good targets, but do not simulate a bombing plane."51 Gliders were considered but rejected, as the Navy had no effective means of getting them up in the air, controlling them in the air, and recovering them afterwards.
The Army Air Corps provided sleeve targets for antiaircraft practices beginning in 1921. A seaplane towed the first sleeves, 16 feet long and 42 inches in diameter, at the end of a 4,000 foot towline. The results were gratifying, with the review board concluding that a red sleeve four feet in diameter and 10 feet 6 inches long, at the end of a 7,000 foot line ". . . in the absence of an actual plane to fire at (provides] the best type of target possible. . ."52 Much later, drones were used, especially to train against dive-bombing attacks, which could be safely simulated in no other way.
In a representative exercise, Mississippi, Nevada, and Pennsylvania fired at sleeve targets in 1922, expending 875 rounds in total. Pennsylvania fired 401 rounds in four runs at a sleeve target (apparently towed by an F5L seaplane flying at about 80 knots) at about 5,000 foot altitude. The course of the sleeve was essentially over the firing ship, as the intent was to simulate a horizontal bombing attack. On run number two, which was typical, 122 rounds were fired in 2 minutes and 5 seconds from 5 guns. Two guns suffered casualties to the recoil cylinders, firing 26 and 28 rounds respectively. One gun, firing 23 rounds, noted several misfires, complaining that "ammunition is very poor," and another fired only 12 rounds, as the pointer could not locate the target. The remaining gun fired steadily with no interruptions, expending 33 rounds. Nobody hit the sleeve.
By 1932-33, at least five methods of antiaircraft control had been developed, direct fire, 1 minute barrage, fixed zone, creeping zone, and creeping barrage. All methods assumed that the target was on a collision course with the firing ship, which implied that concentration fire, which would be virtually impossible to spot in any case, was out of the question.53 The battleline fired three practices that year. Each ship fired Battle Antiaircraft Practice B (for Bombing) twice and Battle Antiaircraft Practice T (for Torpedo) once. Sleeve targets were used for the B practices, towed at about 80 knots, at an average altitude of about 6,300 feet. Once again, as horizontal bombing was being simulated, the course of the sleeve took it nearly over the firing ship. Firing was discontinued once the attacking aircraft - or more precisely, the attacking sleeve - had passed the bomb release point. Runs on the T practice were similar, although the sleeve was towed at low altitude, and the target track was across the bow rather than more-or-less directly across the beam. The results, the observers noted, did not compare favorably with the previous year's performance. Although the overall hit percentage remained constant at 20.3%, the percentage of sleeves hit had dropped from 92% in 1931-32 to only 79% the following year. Curiously, the problem turned out to be due to a sandstorm, with observers noting that the atmosphere during Practice B, which took place off San Pedro, ". . . contained sufficient particles of sand to introduce serious errors in the rangefinding." The best overall performance was turned in by Maryland, which achieved 38+ hits out of 80 rounds fired. The worst performances were turned in by Tennessee and Arizona, which expended 105 rounds and 152 rounds respectively without hitting a thing. The ships averaged 13.35 Shots Per Gun Per Minute.
E.B. Nixon, Commander Battle Force, was unhappy with the results. "The discrepancies between the true speed and altitude of the towing plane and the speed and altitude set on the various rangefinders," he noted, ". . . indicate better than any other single factor that our antiaircraft defense is still in an unsatisfactory state."54
Twenty-four radio controlled drones, converted from N2C-2 and 03U type aircraft were available in 1940. Although many were expended in non-battleship practices, Pennsylvania, Maryland, New Mexico and Mississippi each got a crack at one, and New Mexico shot hers down.55 It was obvious that aircraft capabilities had changed dramatically; target altitudes had been increased from roughly 7,000 to 18,000 feet and further extensions above 20,000 feet were expected. The old 80 knot sleeve targets were gone; directors capable of handling "target presentment" speeds in excess of 200 knots were recognized as both necessary and desirable.
Pre-war estimates of the effectiveness of anti-aircraft gunnery varied dramatically, depending upon who was doing the assessment. One report expected ships equipped with 5-inch batteries to be able, at ranges under 20,000 yards and at altitudes less than 20,000 feet, to break up formation bombing and drive off a high percentage of attacking aircraft. Another commented that "In about 25 percent of the antiaircraft target practices fired against targets simulating attacking horizontal bombers, at an average range of 5,500 yards, the firing vessel [a category including all types] has been able to open tire with sufficient accuracy to place the opening bursts in such a relative position that the target was within the normal pattern in fuze range, elevation and deflection."
In contrast, in 1940, the Director of Fleet Training noted dismally that ". . . the probability of shooting down a single modern horizontal bomber at a range of 5,500 yards as it advances to the attack on a ship mounting a four-gun, 5-inch battery is 2 in 100 chances." The radius of destruction of a single burst, he noted, was not much in excess of five yards, so given four bursts in a 350 yard fuze pattern it was not hard to understand why so few drones were shot down even when the fire control appeared to be perfect.56 Theoretically, even flawless fire control should achieve only about 1% hits. American officers watching European developments noted that contemporary British practice of covering all avenues of approach with a 36-gun density seemed to work well against the Germans, but concluded that success of a similar fire density against the Japanese would have to await the outbreak of actual hostilities.57 American equipment was consistent but unreliable; a study of two identical directors tracking the same target noting that ". . . present antiaircraft fire control equipment is precise, but not necessarily accurate. On a single target presentation, it has been found that solutions obtained by independent control parties will agree closely as to course, speed, and altitude of target, but the solution obtained may not necessarily be a hitting solution."
The results of Pennsylvania's 1940 drone firings seemed to confirm the Director of Fleet Training's pessimism. She fired on two drones without hitting either.58 And if hitting a single drone was difficult, European experience had confirmed that engaging actual aircraft, which would probably approach in formation, would probably be even harder. Air groups which chose to split up, for example, would cause great confusion, as the directors and rangefinders often couldn't agree on which target was which. Granted, enemy bombers would have to straighten out on their final approach, but unlike drones real planes had a nasty habit of changing their speed during the final run to throw off any previously defined solution. One bright spot was the British finding that near misses could often scare enemy bombers away, or at least spoil their aim. Drones, by comparison, were essentially fearless.
The colossal revolution in anti-aircraft gunnery which took place during World War II defies any attempt at succinct description. Changes were massive, in retrospect rather uncoordinated, and the air was (quite literally) so full of authorized and unauthorized innovation that only the most general outline is possible. New gunfire control systems, including a number of significant improvements to the dual purpose Mark 37 gun director, first fitted with Mk 4, then Mk 12, Mk 22 and Mk 28 radars, greatly improved the ability to keep the guns on high-speed aerial targets, and the introduction of the proximity, or VT (Variable Time), fuze eliminated the need to estimate the time of flight and improved the effectiveness of guns by several hundred percent.59
The first full scale tests
of proximity fuzed projectiles fired from a ship at a "live" target took
place on 12 August, 1942, when USS Cleveland fired an exercise
against four radio controlled drones in Chesapeake Bay. The results
were impressive. The first drone crashed due to mechanical failure.
The second and third drones, each making a simulated torpedo run were both
shot down almost immediately, one after an expenditure of less than ten
rounds of ammunition. The fourth drone, on a simulated high-altitude
bombing run, was shot down the next day.60USS
Helena got the first combat kill using proximity fuzes off Munda on
4 January, 1943, bringing down a Japanese bomber with only two 5-inch salvos.
The proximity fuze was introduced gradually, and never completely replaced
the older time fuzes. Granted, proximity fuzes were much more effective
against aircraft, but time fuzes were much cheaper and useful for many
other purposes.61 For a long while,
doctrine prohibited firing VT projectiles where they might land ashore,
lest a sample fall into enemy hands. A special report commissioned
in 1943, when only 25% of 5-inch AA projectiles were fitted with proximity
fuzes, credited them with 50% of the kills on enemy aircraft, and concluded
they were three times as effective as time fuzed projectiles. By
1945, improvements in fuzes and fire control increased this ratio to 6:1.62
Considering the gunnery power of the battle line, the range of most of the torpedoes was almost ridiculously low, and aiming, except in a very general sense, was obviously out of the question.63 The mechanical difficulties in launching a torpedo crosswise underwater at 21 knots - at least prior to World War II - proved to be overwhelming. The percentage of hits was computed on a statistical basis, based on the assumption that the enemy ships, steaming in line, covered a fixed portion of the horizon. In 1922-23, a typical year, the fourteen ships of the battle line fired a total of 116 torpedoes, of which no less than 32 failed to run properly. Two torpedoes ran circular - suggesting that in action the whole exercise might actually have been more dangerous to friend than to foe - while fourteen others either ran "cold" or failed to reach the specified range. One from North Dakota ended up striking the towing ship.
The last battleship torpedo
practices were fired in 1930-31. Maryland, Tennessee,
Colorado,
West
Virginia, California and Idaho each fired six Mk VIII-3
or Mk VIII-3B torpedoes, three to port and three to starboard, at ranges
approaching 11,000 yards. Only West Virginia was able to get all
her "fish" across the target line, achieving two full and three "partial"
hits.64 Unlucky
Idaho had five
erratic runs, and lost one torpedo entirely, placing last. Maryland,
with four full hits, one partial hit, and one "cold shot," placed first.
Each man in her torpedo crew received a $10.00 bonus.
H = 100 / [1 + k(R-2000)]where:
H = percentage of hits
k = 0.00070
R = Range (yards)
This equation would seem
to yield a performance of about 0.165 Hits Per Gun Per Minute (HPGPM) at
the average range of the practices.65
A graph of this equation compared with actual firings from the twenties
and later is reproduced below in Graph 1.
Graph 1 |
We may compare this initial
value of about 0.165 Hits Per Gun Per Minute with the expected performance
of 14-inch batteries in 1935, yielding approximately 0.32 Hits Per Gun
Per Minute, and the standard performance of 14-inch and 16-inch main batteries
in 1940, 0.75 Hits Per Gun Per Minute on the same size target at roughly
equivalent range. The total expected Hits Per Gun Per Minute performance
of 14-inch and 16-inch batteries in 1940 over range is given in Graph 2
below.66
Graph 2 - HPGPM for 14-inch and 16-inch guns Graph 3 - True Mean Dispersion |
While the HPGPM illustration gives a clear snapshot of performance at given dates it is not capable of illustrating any evolutionary trends.67 For any particular year, the heavy dot represents the average performance of ships in the fleet, while the thinner vertical lines extending above and below represent the range between the best and worst performances fired.68 Graph 3 above plots True Mean Dispersion, a measure of the inherent accuracy of the guns. The rather regular "sawtooth" pattern of the average performance line is a function of the type of firing that was done. Low velocity practices, usually fired every alternate year at reduced ranges, had inherently lower dispersion than high velocity practices, where ships fired full charges much farther away.69 The decrease in dispersion taking place about 1934 is evidently due to the introduction of delay coils, which cut the mean dispersion almost in half. The trend is quite well expressed from about 1927 on, and exhibits what might be described as a "classic" evolutionary pattern, comprising a more-or-less steady improvement in average performance coupled with a decrease in the spread of the extreme performances. Gunnery was getting better and more consistent at a relatively constant rate.
Graph 4 below shows the error in the Mean Point of Impact (MPI) over time, i.e., how far center of the average salvo pattern was from the center of the target, is also expressed as a percentage of range. This is a measure of how well the guns were aimed, i.e., of the quality of fleet fire control. As before, average errors, expressed as percent of range, are shown with solid dots, with the thinner lines representing spread between the best and worst ships in the fleet. The trend line (not shown) is indicative of a slow but steady improvement over time. Taken in combination, the graphs seem to show that improving the quality of the guns was easier than improving their aim; the mean dispersion in 1945 dropped 66% from 1920-1945, while during the same time the error in the mean point of impact decreased only 23%. All measurements taken prior to 1945 represent optical spotting. The solid square in the first graph below shows typical results obtained by radar spotting during the war. The relatively poor showing of optical spotting in 1945 show how much radar had taken over by then.
We can combine the two previous figures to come up with an overall assessment of how battleship gunnery changed over the years. Graph 5 below superimposes the mean dispersions evenly over the errors in the mean point of impact. In this graph, the length of the vertical line represents the dispersion, while the distance of the solid dot from the 0% line represents the absolute error in the mean point of impact. Perfection thus would be represented by a thin line falling right along the bottom of the graph. The farther from the bottom line the plot is, and the longer the bar, the worse the gunnery was.
In contrast to our previous
measures, the trend line shows little real improvement over the years.
The performance in the 1926-27 gunnery year was as ghastly as the performance
in the 1934-35 gunnery year was good, but the overall trend is nearly horizontal.
The bars are shorter in later years, indicating that patterns were tightening
- delay coils helped a lot here - but the overall error in the Mean Point
of Impact is nearly constant over time. The best shooting was done
in gunnery year 1934-35.
Graph 4 - Error in MPI Graph 5 - MPI and Dispersion Errors |
A similar plot of HPGPM for
secondary batteries over time shows a slow, steady improvement but it should
be noted that there was an extremely high annual variation. . As
ranges for secondary battery LRBP tended to be constant at about 10,000
yards, a graph gives a reasonable picture of performance variation over
time.
Throughout the period of interest, significant improvements in gunnery represented the adaptation of technology that essentially came from elsewhere. This was not entirely beneficial. The advent and development of aircraft spotting, which revolutionized gunnery in the twenties, was primarily due to innovations in BuAir, not in BuOrd. Similarly, the improvements in weapons effectiveness due to the introduction of radar and the proximity fuze stemmed more from developments in electronics than from stunning advances in ordnance. The development of fire control equipment, while requiring a good deal of input to define the problem, primarily reapplied off-the-shelf optical, electronic and mechanical items in unusual combinations. Within BuOrd itself, research and development was essentially neglected - systematic tests to determine the laws controlling the penetration of armor which might have led to the introduction of more effective projectiles, for example, were rare. Fortunately for the U.S. Navy, this creative sterility seems not to have been confined to America. Although a detailed analysis remains to be written, with the possible exception of the German navy, progress elsewhere, as in the U.S. itself, appears to have been glacially slow.
Clearly, to remain viable, military technology can - and perhaps must - take advantage of technological progress in associated fields. But this can only supplement, not replace, equivalent innovation from within. Established military technology, i.e., technology which has apparently already reached maturity, must continue to allow and even encourage a healthy degree of internal innovation if it is to maintain its vitality in the face of competition from other weapons systems. The tremendous advances in naval gunnery that took place aboard USS Iowa and her sisters in the 1980s were due as much to an environment which allowed, and even encouraged innovation, as they were to the application of new technology. Gunnery in general, and naval gunnery in particular, can continue to prosper only if this creativity is maintained and encouraged. The Navy's "big guns" might have done significantly better in the Persian Gulf, for instance, had they been equipped with Copperhead type guided projectiles, which the Army has had for years.70
Surely, the decline of gunnery
that was associated with the transition to aircraft and missiles was to
a large extent inevitable. Guided flying machines have inherent strengths
(and weaknesses) that are unique unto themselves. But so do guns.
In reality, gunnery failed to maintain its supremacy because it neglected
to seek out and apply the aggressive creativity that would have helped
it to maintain its edge in spite of advances in alternative weapons.
In short, gunnery lost the vision to succeed. Instead of leading,
it went on the technological defensive. Paradoxically, this sad transition
took place during the height of its supremacy, and those minds containing
the fertile seeds of innovation that were crucial to its continued success
either died of neglect in the Bureau of Ordnance, or moved into the cockpit,
leaving the turrets behind. There is a danger that the same thing
may happen again.
Notes:
39 Abridged Range Tables For U.S. Naval Guns, OP 1188, gives the range of the 5"/51 as 17,000 yards at 19°46' elevation. OP 1184 gives only 16,000 yards at 20°32'.
40 Sheets 4 for most secondary battery practices are now lost; this typical firing plan has been reconstructed from descriptions in FTP 191, Orders For Gunnery Exercises, 1940 pp. 2F1 et. seq., and checked against the sheets for the 1939-40 gunnery year, which have survived.
41 The values shown are grand unweighted averages for both forward and after groups in both director and pointer fire (local control). The number of Hits Per Gun Per Minute was computed on the basis of shots in the constructive target, not hits in the much smaller target screen. At 13,000 yards the destroyer constructive target was assumed to be +/- 16 yards in range, and +/-43 yards in deflection. The average range for 1934-35 was about 1.5 times normal, which helps to explain the unusually poor performance that year.
42 FTP-36 (Reports on Gunnery Exercises 1922-23) pp 170.
43 FTP 108 (Reports on Gunnery Exercises, 1929-1930) pp. 113 et. seq.
44 The teething problems with the 5"/38, which has since achieved an almost mythical reputation for accuracy and reliability, seem to have become lost in the fogbanks of history. Commentary in the Reports on Gunnery Exercises series reveals that the "trusty old 5"/38," which jammed constantly at first, was far from a reliable performer when introduced. That, however, is a story for another time.
45 If fired at ranges under about 4,000 yards, the remaining velocity of the projectile was high enough to tear the parachute and extinguish the star.
46 The comparatively low rate of fire with starshells was at least in part due to the requirement to devote at least part of the battery to keeping lit starshells over the target. FTP 140 (Reports on Gunnery Exercises 1932-33) p. 131 gives details. In 1932 special tests were fired to determine if firing starshells deliberately short had the potential to blind an enemy, too. It didn't work.
47 The big problems in using remote searchlights would be in keeping the lights on target when the smaller screening vessel rolled and pitched, and in coordinating the efforts of the firing and illuminating ships. Also, if the illuminating ship were too far away from the firing ship, the relatively narrow searchlight beam would tend to cross the line of fire obliquely, leaving many shorts and overs in darkness.
48 One writer would note in the mid-thirties that "The control . . . is thoroughly unsatisfactory, except in smooth water. The mechanical elevating and training gears are stiff and full of lost motion, and the elevating gear is too slow to follow the rolling of a battleship. It is only under exceptionally favorable conditions that the lights can be controlled from a near-by position, and there is no distant control other than that afforded by the connection to the broadside director training system." The searchlight teams used "match-the-pointer" systems to keep the searchlights nearly "on" in train, but as they usually could not see the target, they had great difficulty in aiming the searchlights vertically. Even a 0.5° pointing error would place the beam 250 feet high (or low) at 5,000 yards. A survey of automatically controlled searchlights aboard California in 1922 showed that although elevation errors were usually very small, azimuth errors were commonly in the vicinity of 3°-4°. Keeping the errors below 2° with the Evershed system then employed required constantly checking the system. In 1929 West Virginia complained that the smallest graduation on the searchlight course dials was 2°, equating to a 200 yard error at 6,000 yards. Still, in 1932 the Director of Fleet Training would note that the greatest difficulty in pointing searchlights was in keeping them on the horizon in spite of the roll of the ship.
49 In 1928 Lt. O. Nimitz summarized the condition of New York's searchlights as follows: "The four high intensity 3-inch searchlights installed in this vessel . . . are in poor condition and require replacement. . . . The ball races and drums are pitted, the frames on the drums require stiffening, and the drums are not light-tight. The doors on the drums need renewal. Covers on ventilating motors are bent or sprung. Signal shutters are bent and warped. Gears on the lamp mechanism are worn. Insulation is poor on electric cables. Ammeters are damaged. Armatures on blower motors are burnt and should be rewound. Thermostatic control mechanism requires some new parts. The lenses . . . are unsatisfactory and will not stand up to gunfire." FTP 99 (Reports on Gunnery Exercises, 1928-1929), pp 932.
50 The range was limited by the maximum time which could be set on the 21 second time fuze of the blunt-point 5-inch/51 caliber illuminating projectile used in the practice. Associated problems with short range firing of starshell, described earlier, meant that this type of projectile was truly effective in only a relatively narrow range band. A long-point illuminating projectile was then under development, which would extend the effective range of illumination out to 7,000 or 8,000 yards.
51 Similar targets - affectionately known as "killer tomatoes" - are used by the battleships today, but only as surface targets.
52 Early experiments are detailed in FTP 36 (Reports on Gunnery Exercises 1922-1923) p. 202 et. seq.
53 In the Direct Method, which became standard during World War II, guns continuously tracked the target. The 1-minute barrage was designed to place a high concentration of fire in a predefined "box" through which the enemy bombers would pass during the last minute prior to releasing their bombs. The Fixed Zone method of predefined a large number of small numbered "zones" around the firing ship, for which correct train, elevation, and fuze settings had been computed prior to firing. The fire control officers then transmitted the number of the zone where the bombers were at any particular time, and the guns fired to the predefined coordinates. The Creeping Zone method was a variation on this theme whereby successive fuze settings were decreased as the target(s) passed through a given zone, thus (to some extent) accounting for the decrease in range. The Creeping Barrage method was simply a 1-Minute barrage which was applied more or less continuously. Similar methods were used in surface fire control as well. For detailed descriptions, see FTP 134, Gunnery Instruction, 1933.
54 FTP 140 (Reports on Gunnery Exercises 1932-33) p 245. The average error was about 200 feet in altitude, and only one or two knots in speed, but this masks the fact that due to coincidence the overestimates and underestimates nearly cancel. The average absolute error was almost twice as great. Better spotting should have corrected these initial errors, at least in altitude, almost immediately.
55 Expending 54 5-inch rounds in the process. Maryland expended 56 rounds and hit the drone twice. Mississippi expended 96 rounds in two runs. Her drone eventually crashed, but the cause was probably unrelated to firing. Pennsylvania fired 94 rounds in two runs and never hit a thing.
56 The quality of ammunition certainly was no help here; observers typically noted somewhere between 20% and 35% "low order" detonations, and between 4% and 20% duds, this with 45 second Mk VIII-3 time fuzes. The average four-gun fuze pattern was about 400 yards in range.
57 See FTP 203-1 (Reports on Gunnery Exercises 1939-40) pp 95 et. seq. for more detail.
58 Pennsylvania's actual director settings as compared to information provided from the drone are reproduced below:
Altitude (ft) Course (deg)Speed
(knts)
Run No.1
Drone Actual
11,800
145°
131
Pennsylvania Estimate
12,200
163°
86
Run No.2
Drone Actual
10,200
134°
121
Pennsylvania Estimate
10,200
156°
96
Noting these results, her gunnery officer correctly noted that their "best forte" was some previous knowledge of the probable speed characteristics of the target. The error in course estimation seems large, but poor control of the drone meant that it quite typically (and unpredictably) would wander 10°-15° off the average course.
59 The Mark 37 director system, which weighed almost 20 tons (and which could, in any case, engage only a single target at a time), was originally designed to control the fire of groups of guns in surface salvo fire and was not easily adapted to World War II anti-aircraft work where it might have to handle multiple rapidly-maneuvering targets approaching from several directions at once. The limitations of the Mk 37 were acceptable when barrage fire was common, but VT fuzed projectiles were so effective that AA batteries could henceforth be "split" in order to engage several targets simultaneously. This new potential to assign individual guns to individual targets led to the development of new anti-aircraft directors such as the Mark 57, and the (much smaller) Mark 51. For a fine summary of directors introduced during World War II, see Friedman, Naval Weapons of World War II, USNI Press, c. 1984 [Transcriber's Note: John Campbell is the correct author of this book. The author of this article may have meant to refer to Friedman's Naval Radar or US Naval Weapons].
60 See Baldwin, Ralph, The Deadly Fuze - Secret Weapon of World War II, Presidio Press, 1980.
61 USS South Dakota, for example, was still expending "old" Mk 18 mechanical time fuzes in anti-aircraft target practices in May and June 1945. The bursts of time fuzed projectiles were useful in pointing out the target to other ships, were likely to frighten or distract enemy pilots and enabled the relatively rapid detection of grossly inaccurate fire control solutions. Even after the war, doctrine suggested that the ratio of time fuzed to proximity fuzed projectiles should normally be about 1:1.
62 Baldwin, Ralph, The Deadly Fuze, pp 245. According to Baldwin, an analysis of 278 aircraft shot down by VT fuzed projectiles between October, 1944 and August, 1945 indicated that only 46 of these would have been destroyed if time fuzed projectiles had been employed. Baldwin's 6:1 ratio apparently assumes that 70% of the VT fuzes worked. A 50% failure rate - the Navy's lower limit of acceptability - meant the effectiveness ratio was closer to 4:1. In comparison, mechanical time fuzes such as the Mk 18 typically worked about 90%-95% of the time. Operational considerations re the application of VT fuzes are well summarized in OP1480, VT Fuzes For Projectiles and Spin Stabilized Rockets, 15 May, 1946.
63 A mixture of Mark VIII, Mark IX and Mark X torpedoes were fired in 1922. The Mark VIII, the best of the bunch, could only reach 16,000 yards at 36 knots, taking over 13 minutes to arrive. For a five minute run, this meant that the opposing battle-line would have to have been only 5,500 yards abeam, so torpedoes were evidently intended only to finish off cripples that could not shoot back. In 1922, Admiral Jackson, Commander Battleship Squadron Four, confirmed this, noting, "The range of the Mark IX-I torpedo [7,000 yards at 27 knots] is too short to be of great value as an offensive weapon excepting under extraordinary circumstances." The 36 knot, 3,500 yard, Mark X was even worse.
64 Exactly what constituted a "partial hit" is unclear; presumably this was a hit which reached the target line, but passed between the target rafts. At 11,000 yards the number of torpedoes which passed under a target raft as opposed to those passing between two rafts must have been entirely a matter of luck, i.e., a function of the size of the rafts and distances between them. For the record, West Virginia's errors were 655 yards left, 475 yards right, 1,062 yards left, 77.5 yards right, and 632 yards left. The error of the sixth torpedo is unrecorded; presumably it missed the target train entirely.
65 The equation yields about 11% hits at 13,783 yards, which was the average range at which the exercises were fired. The time to complete the firings is not recorded, but assuming a rate of fire of 1.5 Shots Per Gun Per Minute, this equates to 1.5 x 0.11 = 0.165 Hits Per Gun Per Minute. The 1935 figures for HPGPM are adapted from tables in the 1935 Maneuver and Fire Rules, the 1940 figure for HPGPM from the 1940 Orders For Gunnery Exercises. The graphed line for 16-inch percentage hits for 1940 was also adapted from the 1940 OGE booklet, obtained by dividing standard Shots Per Gun Per Minute (SPGPM) by twice the Hits Per Gun Per Minute in the Control Zone (HPGPMCZ) which should have caught half the shells. The improvement in accuracy, especially at moderate ranges, is dramatic.
66 The U.S. Navy never reverted to a smaller caliber after adopting the 16-inch gun. The 14-inchers never shot as accurately as their 16-inch successors, a problem which defied more than twenty years of concentrated effort to cure. Probably, the interior ballistics were wrong. According to Bulletin of Ordnance Information No.2, 1945, pp 29-30, the then-standard nine-gun range pattern for the 14-inch was 2.03% of range as opposed to 1.9% for 16-inch weapons.
67 Plotting mean dispersion vs. range instead of pattern size vs. range yields figures more susceptible to advanced analysis. Fortunately, converting the true mean dispersion, D, to other (possibly more familiar) measures of accuracy is relatively easy:
D x 0.846 = Probable ErrorThe equations required to convert the True Mean Dispersion to pattern size are complex, and are not given here. For normal numbers of guns, the conversion values are approximately as follows:
D x 1.692 = 50% Zone
D x 1.2545 = Standard Deviation
Number of
Ratio of Pattern
Guns (n)
Size to True Mean Dispersion
1
1.00
2
1.69
3
2.43
4
2.89
5
3.21
6
3.47
7
3.67
8
3.85
9
4.00
10
4.13
11
4.24
12
4.34
To convert True Mean Dispersion
values to hitting percentages at various ranges, change the True Mean Dispersion
as a percentage of range to an absolute value, convert this actual value
to a probable error and then use the dispersion rectangle shown below to
convert the probable error into a hit percentage given a target of known
size.
 |
The dispersion rectangle expresses the percentage of shots falling in any given sector of a pattern. The percentages along the edges of the rectangle represent the totals of the respective rows and columns. The mean point of impact is at the center of the diagram and each row and column is one probable error wide. All shots are assumed to fall within +/- four probable errors of the mean point of impact. The diagram shows, for example, that a rectangle adjacent to the mean point of impact one 50% zone long and one 50% zone wide will catch 25% of the shots (6.25 + 6.25 + 6.25 + 6.25 = 25.00). A target one probable error wide and one probable error deep located four probable errors away from the mean point of impact in both range and deflection is at the corner of the diagram, and will catch 0.04% of the shots, a one probable error by one probable error sized target three probable errors behind the point of impact will catch 1.75% of the shots.
Suppose, for example, that the True Mean Dispersion was 1% of range and it was desired to compute the hit percentage against a battleship sized target at 25,000 yards. Assume that the Mean Point of Impact to be centered on the target, that a pattern is 2 mils wide in deflection, and that the target is 600 feet long and 180 feet wide, including the danger space.
The True Mean Dispersion is 1% of 25,000 yards, i.e., 250 yards. The probable error is 0.846 times the danger space, or 212 yards. The 180 foot (60 yard) wide target is 60/212 = 0.283 probable errors deep in range. The deflection pattern is 2 mils wide, i.e., only 25,000 x 0.002 = 50 yards across, so we may assume that all projectiles hit in deflection. Near the mean point of impact (and assuming no misses in deflection), the dispersion rectangle shows that one probable error catches 25% of the shots, so a space 0.283 probable errors wide may be assumed to catch approximately 0.283 x 25 = 7.075 percent of the shots fired.
68 Data on best and worst performances prior to c. 1925 are lacking, so the curves in this area are based on very "thin" data.
69 Low velocity or reduced charge practices were fired at velocities of about 2,000 f/s; high velocity, full charge practices were fired at velocities of about 2,600 f/s. The trend line of ranges for the high velocity practices is interesting, climbing from c. 21,000 yards in 1921 to about 27,000 yards by the mid-thirties. The decrease in Long Range Battle Practice ranges after that date is interesting too, but all of these were low velocity practices.
70
Development of a 13-inch subcaliber round for the Iowa class battleships,
which could have been developed into a Copperhead variant, has apparently
been discontinued.
-5.gif){kind=small}