Japanese Antiaircraft Guns, WWII Tactical and Technical Trends, No. 12, November 19, 1942 (Lone Sentry)

The following is a preliminary report based on recent examination of captured Japanese antiaircraft artillery weapons.

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a. 75-mm AA Guns

The Japanese had three AA gun batteries of four guns each emplaced around their flying field and installations. They were placed in a generally triangular formation about 4,500 yards on a side. These guns were 75-mm on navy pedestal mounts. They have 360° traverse and 75° elevation. They fire HE shell with 30-second mechanical time and percussion fuzes.

There were no directors. At each position there was a 68-inch base coincidence range finder, navy type. Each gun has two telescopic sights mounted one on each side, with traversing handwheel on the right and elevating handwheel on the left. Lateral deflection, vertical deflection, slant range, and superelevation are all set on the series of drums, disks, and dials on the left side of the mount. The lateral deflection drum turns on a spiral, and the scale is graduated from 0 to 200. The slant-range drum has two scales; the outer scale is graduated from 0 to 7,000; the inner scale has a graduation of 100 opposite the 0 on the outer scale, and 300 opposite 6,000 on the outer scale. This range drum is rotated by a small handwheel. Inside the range drum is a disk which is rotated by another small handwheel which also moves a pointer laterally as the disk rotates. On the disk, covering about 1/6th of the surface, are curves graduated from 500 to 5,000 in units of 500, believed to be superelevation curves. All of this moves both lateral and vertical sights as the drums and disk move. In addition there is what appears to be an open sight mounted on a drum. This drum is graduated from 0 to 100 in each direction. The handwheel which turns this drum elevates or depresses the vertical sight only.

There was no fuze setter such as ours. There were two hand tools, one similar to a pair of long pliers with tits on each end which fit in the two slots on the bottom ring of the fuze, below the graduations. The other tool was shaped like a truncated cone, with handles on each side. It had a slot in one side which fits over the lug protruding from the side of the fuze. The fuze was set by holding with the first tool and rotating the second. It is not clear where the fuze setting was obtained. It may be from the inner scale on the range drum which was graduated from 100 to 300. No charts were found which would seem to be used for obtaining fuze setting.

b. AA Machine Gun, Caliber .50

Near the gun position on the beach was a Japanese machine gun, caliber .50, air-cooled and gas-operated. It was fed by semicircular clips holding 30 rounds each. Both ball and tracer ammunition was found. The machine gun had a forward area sight, oval in shape, about 5 inches across by 3 inches high, with a small oval in the center about 1 inch across by 0.6 inch high. The vertical and lateral wires in this sight went all the way across, while the diagonal wires on each side went only from the outer to the inner oval. The rear sight was a small vertical rod with a ball tip.

c. 25-mm Gun

In a separate position along the beach was a pompom, about 25-mm* with three barrels. This was the newest and most modern AA equipment seen. The sighting system was on the same general principles as that of the 75-mm guns. There were two telescopic sights, one on each side. All other sighting equipment was on the left side. Lateral and vertical deflection are set on a kind of hemisphere. The lateral handwheel rotates the hemisphere; graduations around the lower edge are from 0 to 180 in each direction. There is a slot about 1/2 inch wide up one side, across the top, and down to the other side of the hemisphere; in this slot, a kind of streamlined, elongated bird sight slides. The slot is graduated from 0 at the top to 50 on each side. Time did not permit a thorough examination of this sighting equipment, so that it is not thoroughly understood. Range is set by either of two handwheels. One rotates a drum with scale graduated from 500 to 3,800 in red numerals. The other rotates a drum with scale graduated from 0 to 3,800 in blue numerals. The guns are fed by clips which hold about 15 or 20 rounds AP and tracer.

In operations against the Japanese in this theater, our fighters have reported accurate AA gun fire up to about 12,000 ft. A hurried study of this 75-mm AA gun equipment would seem to indicate that this is about the limit of accurate fire with this equipment. Captured Japanese aviators have expressed wonder and admiration of the accurate high-altitude AA gunfire of the Americans. One 90-mm AA gun battery shot down a Japanese bomber at 27,400 feet altitude.

* Although reported as about 25-mm, it is possible that the gun is a standard Japanese 20-mm.