Oldsmobile gun first used on P-39 airplanes. Some of these guns were salvaged from crashed aircraft and installed on PT boats to give these small craft a "barge buster" weapon. This proved successful and new guns were produced specifically for use on PT boats.
Action was long-recoil (Browning-type). Used a vertically-sliding breech block and percussion firing.
Nomenclature Note: This weapon was originally designated as the T9. Designation changed to M4 about 1942.
Later in the war the more powerful 37 mm M9 was developed. This weapon fired a larger, heavier round and a few were used on PT boats.
Unless otherwise noted, the data below is for the M4.
|Designation||37 mm/56 M4|
|Ship Class Used On||PT Boats|
|Date Of Design||about 1937|
|Date In Service||1942 (on PT Boats)|
|Gun Weight||Without breech: 55 lbs. (25 kg)
With breech: 213 lbs. (97 kg)
|Gun Length oa||89 in|
|Bore Length||about 81.6 in (207.2 cm)|
|Barrel Length||65 inches (165 cm)|
|Length Of Rifling||N/A|
|Rate Of Fire||Cyclic: 125 to 150 rounds per minute|
|Weight of Complete Round||N/A|
|Projectile Types and Weights||HE: 1.34 lbs. (0.61 kg)
AP 1: 1.66 lbs. (0.75 kg)
|Cartridge Case Type, Size and Empty Weight||Brass, 37 x 145R mm, N/A|
|Propellant Charge||0.15 lbs. (0.070 kg) NC|
|Muzzle Velocity||HE: 2,000 fps (610 mps)
AP: 1,825 fps (556 mps)
|Working Pressure||10.4 tons/in2 (1,638 kg/cm2)|
|Approximate Barrel Life||N/A|
|Ammunition stowage per gun||N/A 2|
|Effective||about 4,000 yards (3,660 m)|
|Maximum||8,875 yards (8,115 m)|
- "Naval Weapons of World War Two" by John Campbell
- "US Naval Weapons" by Norman Friedman
- "Rapid Fire" by Anthony G. Williams
- Bill Maloney Website
- Pictures and data about 37 mm gun on PT-617
- 09 November 2007
- 06 March 2009
- Added recoil length