This weapon was manufactured by Rheinmetal-Borsig and was essentially a longer barrel version of the Army 3.7 cm Flak 36. This new gun was a great improvement over the older 3.7 cm/83 SK C/30 and had a much higher rate of fire. Recoil operated, air cooled and used five-round ammunition strips.

These were the first Kriegsmarine light anti-aircraft guns to have shields, a surprising shortcoming of earlier weapons.

The design of this gun emphasized ease of manufacturing. Constructed of a monobloc barrel which was connected to the breech ring by a bayonet joint to allow easy replacement. Used a vertical sliding breech block, hydraulic brake and spring recuperator.

Gun Characteristics

Designation 3.7 cm/69 (1.5") Flak M42
Ship Class Used On U-boats, Emden, destroyers and minesweepers
Date Of Design 1942
Date In Service 1944
Gun Weight 240 lbs. (109 kg)
Gun Length oa N/A
Barrel Length 100.79 in (2.560 m)
Rifling Length 90.1 in (2.289 m)
Grooves (20) 0.0217 in deep x 0.150 in (0.55 mm x 3.81 mm)
Lands 0.087 in (2.2 mm)
Twist Uniform RH 1 in 25.6
Chamber Volume 16.5 in3 (0.270 dm3)
Rate Of Fire 160-180 rpm rounds per minute cyclic
60 rpm practical


Type Fixed
Weight of Complete Round HE tracer: 3.0 lbs. (1.36 kg
HE incendiary: 3.02 lbs. (1.37 kg)
AP tracer: 3.31 lbs. (1.50 kg)
Projectile Types and Weights HE tracer: 1.40 lbs. (0.635 kg)
HE incendiary: 1.42 lbs. (0.640 kg)
AP tracer: 1.54 lbs. (0.700 kg)
Bursting Charge HE tracer: N/A
HE incendiary: N/A
AP tracer: N/A (probably solid bullet)
Projectile Length N/A
HE incendiary, complete round: 14 in (355 mm)
Propellant Charge 0.386 lbs. (0.175 kg) RPC/38N
Cartridge Case Type, Size and Empty Weight Brass, 37 x 248R, N/A [1.0 lbs. (0.51 kg) loaded]
Muzzle Velocity HE tracer: 2,838 fps (865 mps)
HE incendiary: 2,772 fps (845 mps)
AP tracer: 2,674 fps (815 mps)
Working Pressure 18.7 tons/in2 (2,950 kg/cm2)
Approximate Barrel Life 7,000 rounds
Ammunition stowage per gun 2,000 rounds 1
  • ^Minesweeper outfits were half AP tracer and half HE tracer. Outfits on other ships was intended to be two-thirds HE incendiary and one-third AP tracer.
  • The sources below differ in many areas for this weapon. The figures given in this table come mainly from "Naval Weapons of Word War Two."


Range with 1.34 lbs. (0.61 kg) HE Incendiary
Elevation Distance
45 degrees 7,000 yards (6,400 m)
AA Ceiling @ 85 degrees 17,750 feet (4,800 m)

Tracer range was 5,250 yards (4,800 m).

Mount / Turret Data

Designation Single Mount for U-boats: Ubts. LC/39
Single Mount for Surface Ships: Flak LM/42
Twin Mount for U-boats: Ubts. Dop. LM/42
Twin Mount for surface ships: Dop. LM/42
Weight Ubts. LC/39: N/A
Flak LM/42 with shield: 2,980 lbs. (1,350 kg)
Twin: 3,860 lbs. (1,750 kg)
Elevation -10 / +90 degrees
Elevation Rate Manual operation, only
Train 360 degrees
Train Rate Manual operation, only
Gun recoil N/A
  • Shields on U-boat mounts were fitted with hinge points such that they could be folded back against the barrels in order to reduce water drag. Surface ship mounts had more complex shapes and did not fold.

Additional Pictures


"Naval Weapons of World War Two" by John Campbell
"German Warships 1815-1945" by Erich Gröner
"Das Buch der Deutschen Kriegsmarine" by Jak P. Mallmann Showell
"German Naval Guns: 1939 - 1945" by Miroslaw Skwiot
"German Destroyers of World War Two (2nd Edition)" and "German Cruisers of World War Two" both by M.J. Whitley
Special help by Dave Krakow and Anthony G. Williams

Page History

15 May 2006 - Benchmark
20 May 2012 - Updated to latest template
23 March 2013 - Redid photograph of Z39
23 April 2020 - Converted to HTML 5 format, reorganized notes, added data and photograph of U-190