The 3.7 cm Flak M42 was the marine version of the 3.7-centimetre (1.5 in) Flak 36/37 and used by the Kriegsmarine on surface ships and as the M42U on Type VII and Type IX U-boats.

The 3.7 cm Flak M42U used several types of mounts and entered service in autumn 1943.

The gun was loaded with a five-round ammunition clip, giving it a rate of fire of 250 rounds per minute, unlike the SK C/30 which was single-shot with a rate of 30 rounds per minute.

The M42 was also about 134 kg (295 lb) lighter than the SK C/30 and had gun shields.

[1][3] The LM 42U mount was developed specifically for the 3.7 cm Flak M42U.