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) |
| Rifling Length | N/A |
| Grooves | N/A |
| Twist | N/A |
| Length Of Rifling | N/A |
| Chamber Volume | N/A |
| Rate Of Fire | Cyclic: 125 to 150 rounds per minute |
| Type | Fixed |
|---|---|
| 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) |
| Bursting Charge | N/A |
| Projectile Length | N/A |
| 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 |
| Elevation | Range |
|---|---|
| Effective | about 4,000 yards (3,660 m) |
| Maximum | 8,875 yards (8,115 m) |
| Designation | Modified 3-pdr pedestal type |
|---|---|
| Weight | N/A |
| Elevation | N/A |
| Elevation Rate | Manually operated, only |
| Train | 360 degrees |
| Train Rate | Manually operated, only |
| Gun recoil | 9.5 in (24 cm) |
"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 - Benchmark
06 March 2009 - Added recoil length
30 June 2024 - Converted to HTML 5 format