| General Notes
There are two major classes of ASW projectiles;
proximity and contact weapons. The former, such as the depth charge,
must be large enough to damage a submarine even at a great distance.
The nuclear depth charge - such as used on ASROC and SUBROC - achieves
the greatest kill radius, but has obvious political consequences.
Contact weapons, such as Hedgehog and Squid, can be much smaller, but must
be either guided into their targets or else used in very large numbers
in order to obtain a kill. A homing torpedo is an intermediate case,
since - in theory - its effective homing volume may be comparable to even
a nuclear depth charge.
Depth charges were first developed by the
British
Royal Navy in 1916. In February 1917 the USN Bureau of Ordnance
began production of the first USA depth charge, the Mark 1. The USN
was unimpressed with the British method of using a sling which held a single
depth charge, so instead designed a rack capable of holding multiple charges.
This first depth charge rack, designated as the USN Mark 1, was quite successful
and was widely used by the British and French navies during the rest of
the war. The USN agreed in 1917 to produce 15,000 of the British
Type D depth charge for the Royal Navy, although the Type D was considered
to be inferior to the USN's own Mark II, as the Type D had a tendency to
explode prematurely when used with a projector.
Dropping depth charges off the stern via
a rack or track was standard practice for ASW vessels in both World Wars.
For the heavier depth charges, such as the Mark 4 and the Mark 7, this
was the only method used, while the smaller depth charges could be used
with "Y" and "K" guns. Destroyer and Destroyer Escorts generally
had two racks while smaller ships had one.
Relatively little research work on ASW
weapons was undertaken during the interwar period, the most significant
effort being a 1936 study by the Special Board on Naval Ordnance which
showed by mathematical analysis that depth charges with 600 lbs. (272 kg)
charges would always be more effective than those with 300 lbs. (136 kg)
charges even when the smaller number of the heavier type that could be
carried was taken into account.
Projectors for depth charges and ahead-throwing
projectors for Hedgehogs, Mousetrap and various signal and flare projectors
formed a single Mark series. Later ASW Rocket Launchers were included
in the general Rocket Launcher series. The two most significant ones
are detailed below.
"Blind Time" is the time between when a
weapon is launched and when it reaches the target location. In addition,
most early sonar systems lost the target submarine on close approach, usually
requiring a "sprint" to reduce blind time. For depth charges, this
meant that they were dropped or fired after the sonar contact was lost.
Hedgehog was the first "ahead-fired" weapon that could be used while the
attacking ship still had sonar contact on the target submarine. This
reduced the blind time by two-thirds when compared to depth charges.
The USA built a total of 622,128 depth
charges between December 1941 and September 1945. This figure does
not include Hedgehog, Mousetrap and experimental units not placed in service
use. Over half of these depth charges were still on hand when hostilities
ended.
USN ASW effectiveness during World War
II
In the first few months of the war only
5 percent of all depth charge attacks were successful. Normal combat
conditions reduced that figure to 3 percent. Combat records showed
that in early 1942 the lethal probability of a single depth charge pattern
(barrage) was about 3 percent and five attacks would raise the chance of
a kill to about 10 percent. The possibility of inflicting significant
damage to a submarine was about 30 percent after five attacks. By
the end of 1943, better weapons and tactics had improved these figures
such that about 30 percent of all detected submarines suffered at least
some damage and 20 percent were killed. By the last year of the war,
at least 35 percent of all submarines attacked were being damaged while
30 percent were killed. In mid-1944, the USN was claiming an 8 percent
kill rate with a single Hedgehog pattern. By the middle of 1945,
that figure had risen to 10 percent.
In the Atlantic Theater, US surface ships
sank 60 submarines, shore-based aircraft sank 54, ship-borne aircraft sank
32 and 40 were destroyed by bombing raids on yards and bases. In
the Pacific Theater, surface ships sank 60 Japanese submarines, shore-based
aircraft sank 3.5 and ship-borne aircraft sank another 9.5.
USN ASW torpedoes are listed in the Torpedo
section of Naval Weapons. |
