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Home » U-Boat Weapons » Antiaircraft Guns

Antiaircraft Guns

2cm Flakzwilling 37mm Flak 38

At the start of the war, the standard U-boat antiaircraft armament was a single 20mm Flak (Flugabwehrkanon) gun mounted on the main deck, far from the conning tower. The setback was that the conning tower itself created a large dead zone, and the gun had to be removed and stowed before diving, increasing the amount of time needed to dive. Eventually the weapon was relocated to a special platform just aft of the bridge.

By mid 1942, allied airpower had increased significantly, and it became clear that a heavier air defense armament was required. As a result of this, twin and even quadruple 20mm mountings were installed. But as a result of delays, it was not until the middle of 1943 that the first twin and quadruple mountings appeared. At about the same time, new 20mm shells were also introduced, which not only carried three times more explosive than previous shells, but the explosive itself was new and much more powerful. By late 1943, the new and much more powerful 37mm Flak gun made its debut. This was a navalized version of the German army Flak 37 which was quickly adapted and installed on U-boats. Problems were encountered with the 37mm gun as well, as it was very sensitive to seawater and frequent stoppages meant that it had to be serviced regularly. Finally when this too proved inadequate to thwart air attacks, it was recognized that U-boats were unlikely to win combat engagements with aircraft, and the best defense was to spot an aircraft in time to crash dive to safety.

U-118, a Type XB under attack 20mm flak on a Type IX.
U-118, a Type XB minelayer under attack from ASW aircraft of the USS Bogue. She sank shortly after this attack. A U-boat crew mans the 20mm flak on a Type IX.

2cm Flak 30

Developed by Rheinmetall Borsig, the 2cm Flak 30 entered service in the early 1930s and was in effect a large machine gun. It was a recoil operated weapon and had two triggers side by side; the right for single shots and the left for automatic. It fired a variety of ammunition, from armor piercing to explosive shells and was usually coupled with tracers. The effective rate of fire was 120 rounds per minute.

2cm Flak 38

Developed by Mauser, this was essentially the same as the 20mm Flak 30, but with an improved bolt which nearly doubled its rate of fire. This version was installed in twin (Flakzwilling) and quadruple (Flakvierling) configurations, and had a rate of fire of 400 and 800 rounds per minute.

3.7cm Flak 42

This was the final antiaircraft gun developed for U-boats. Adapted from the German army 37mm Flak 42, it had a further range and fired a much more powerful shell. The rate of fire was somewhat lower at 50 rounds per minute.

U-boat Flak Gun Specification
  20mm Flak 30 20mm Flak 38 37mm Flak 42
Year Introduced 1930 1938 1942
Caliber 20mm (0.79in) 20mm (0.79in) 37mm (1.46in)
Traverse 360 degrees 360 degrees 360 degrees
Elevation -2 to +90 degrees -2 to +90 degrees -10 to +80 degrees
Rate of Fire
(per minute)
120 rounds 220 rounds 50 rounds
Ammunition Weight 0.32kg 0.32kg 0.73kg
Clip Size 20 rounds 20 rounds
Reload Time 5.5 seconds 5.5 seconds
Breech Automatic Automatic Automatic
Effective Range 12,350 meters 12,350 meters 15,350 meters

U-995 German Type VIIC U-Boat

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