1) IS is my abbreviation for the Type 3 Common incendiary shrapnel round (sankaidan) intended for AA use.  Fuzes for these were set in the shell handling room with fuze protectors used to prevent damage before loading.  Type 3 Common may have made up as much as 40% of the outfit by 1944.  See below for more information.

2) Type 91 shells were all 6 / [infinity] crh with boat tail.  The diameter of the bourrelet was 18.07 in (45.898 cm).  The original Type 91 APC was L/4.25 or 76.9 inches (195.35 cm) long.  The later Type 1 version was L/4.47 or 81 inches (206 cm) long.  The main difference was the length of the windscreen, as the conic angle went from 23.5 degrees to a longer, sharper 21 degrees.  Type 1 shells also introduced a dye bag, which may have slightly increased their weight over that of the Type 91.  The base of the Type 1 was slightly different from the Type 91 as the original two driving bands were replaced by a single double-width band with a copper ring in the middle of the band.  The modified type superseded the original in 1941, so these battleships may never have carried any but the newer shell.  See the additional photographs page for a sketch of the Type 91.

3) Each mounting held 300 rounds with 180 rounds stored in two handling rooms on the rotating structure and the remaining 120 in shell rooms.  The practice was to feed projectiles from the lower handling room until the supply was exhausted and then feed from the upper handling room.

4) The propellant charge was in six bags.  Bags were made of wool until 1942 at which time silk ones were substituted.  Bags had a 1.1 lbs. (0.5 kg) separate silk bag of gunpowder at one end.

5) Smaller propellant charges were available for training and target rounds.  These were designated as "Reduced" and "Weak" charges.  "Reduced" charges gave about two-thirds of the normal service velocity and were rated at 0.25 ESR while "Weak" charges were rated at 0.5 ESR.  No muzzle velocity is given for "Weak" charges.

The concept behind these shells was that the ship would put up a barrage pattern through which an attacking aircraft would have to fly.  However, these shells were considered by US Navy pilots to be more of a visual spectacular than an effective AA weapon.

1) These mountings had a unique sliding cross-head for the elevating cylinder anchor point.  This could be set to allow either -5 to +45 degree elevation or +3 to +41 degree elevation.  The advantage of this was that the latter setting meant that no locking pins had to be inserted to hold the guns at the loading angle, the operator merely kept the controls at the "depress" position until an indicator showed him that loading was complete.  This sped up the loading cycle and, as shown in the range table above, cost very little in terms of maximum range.

2) These turrets had two independent sets of training gear, only one of which was in use at a time.  Each was driven by a 500 hp vertical swashplate motor driving a train of straight-toothed pinion gears.  Guns were individually sleeved.

3) The gun axes were 137.8 in (350 cm) apart.

4) The center gun had a 0.080 second firing delay to reduce shell dispersion.

5) Each gun had its own pusher shell hoist and cordite cage hoist.  The cylindrical flashtight charge container held all six charges in line, allowing a single rammer stroke to load the gun.  Two auxiliary hoists were fitted in each turret.  Both shells and propellant bags were hoisted vertically in suitable containers.  Transfer of shell in the gunhouse was effected manually by overhead travellers and chain purchase.

6) The following excerpt is taken from US Naval Technical Mission to Japan report O-45(N):

The 46 cm (18-inch) triple mount was the first large mount ever designed and produced by the Japanese which was not practically identical with the large British mounts prior to World War I and built for the battleship KONGO.  In almost every part of the 18-inch mount a complete departure from this old design was made.  For shell and powder hoists the Japanese 18-inch mount was copied [sic, but probably meant 16-inch mount], but, generally speaking, the mechanisms were unique.  Compared with British and U.S. practice, (16-inch, 14-inch and 8-inch), the mount was simple in design.  It had no complicated hydraulic safety interlocks and comparatively few mechanical ones.  Reliance was placed on good drill to avoid accidents.  Even taking into account the size of the gun, the general impression gathered is that an unduly large factor of safety had been allowed in the design of the turret machinery as a whole, resulting in a very heavy mount, the total revolving weight of one turret being 2,510 metric tons [2,470 tons].

A very satisfactory rate of fire was obtained for a gun of this size:  1.5 rounds per minute at full elevation.  A maximum range of slightly under 46,000 yds was obtained with a 3,220 lb shell.

The most interesting features of the mount were (a) the method of stowing and moving shells about the shell and shell-handling rooms using a fairly simple, but bulky and heavy mechanism; (b) the powder cage and rammer, designed to enable a full charge to be loaded by a single rammer stroke; and (c) the attachment of the elevating piston rod to the slide which was designed to avoid the necessity for a complicated slide locking gear, and to reduce the loading cycle time by cutting out the time usually required for locking and unlocking the slide.

Other mechanisms worthy of note are as follows:

    1) The powder bogie and mechanisms for transferring powder from the fixed to the moving structure.
    2) The gunhouse bogie and rammer.
    3) The wormless training gear, with its "coaster" gear substitute for the normal friction discs.
    4) The electric cable leading-in gear.

It was stated by the Japanese that considerable attention had been paid to flashtightness throughout the turret.  Although this was probably not up to U.S. and British standards, it is difficult to give a definite opinion on this point without having seen a completed turret.  The performance of the turret in service was considered by the Japanese to have been very satisfactory with the exception of the large quantities of lubricating oil, which the Japanese could ill afford, were required by the training and powder hoist gears.  Spreads of salvos were reasonably small, (about 500 to 600 yards at maximum range).  The blast effect, particularly on the bridge, was found to be very severe.

Without having seen one of these turrets in operation or even a completed turret, an opinion will not be expressed on its probable performance or its value as a weapon beyond that already given above.  The statements of the Japanese, however, are considered to be well-founded.