These were a series of built-up guns dating back to the 1890s. This was the standard anti-torpedo boat gun of the late pre-dreadnoughts, armored cruisers, destroyers and submarines. Fired fixed ammunition.
Bethlehem Steel provided twelve guns to Britain during World War I which were known as the 3"/8cwt. Six additional guns, details unknown, were designated as 3"/17cwt.
During World War II about 350 guns were supplied as part of Lend-Lease. These were used mainly on DEMS and on three ex-"R" class submarines.
Mark 2 was a built-up weapon with a side-swing carrier breech. The Mark 3 was of simpler construction but otherwise similar. Mark 5 had uniform rifling and a Driggs-Seabury semi-automatic vertical sliding breech mechanism. Mark 6 was similar but with a longer recoil slide. Mark 8 was a Mark 6 with a horizontally instead of vertically sliding breech block and only one of these guns were built. Mark 6 Mods 4, 5, 6 and 7 were "wet guns" for submarines. Mod 6 had a chrome plated slide surface and rear cylinder while the other exposed parts were painted.
| Designation | 3"/50 (7.62 cm) Marks 2, 3, 5, 6 and 8 |
|---|---|
| Ship Class Used On | Many ships 1900-1920s |
| Date Of Design | about 1898 |
| Date In Service | 1900 |
| Gun Weight | Mark 2: 2,086 lbs. (946 kg) with breech
Mark 3: 1,986 lbs. (901 kg) with breech Mark 5: 2,280 lbs. (1,034 kg) with breech |
| Gun Length oa | N/A |
| Bore Length | 150.3 in (3.816 m) |
| Rifling Length | N/A |
| Grooves | 24 |
| Lands | N/A |
| Twist | Marks 2 and 3: Increasing RH 0 to 1 in 25
Mark 5 and Mark 6: Uniform RH 1 in 25 Mark 8: N/A (probably same as Mark 5) |
| Chamber Volume | N/A |
| Rate Of Fire | 15 - 20 rounds per minute |
| Type | Fixed |
|---|---|
| Weight of Complete Round | 24 lbs. (10.9 kg) |
| Projectile Types and Weights | Common: 13 lbs. (5.9 kg)
AP Mark 29 Mods 1 and 2: 13.1 lbs. (5.9 kg) |
| Bursting Charge | Common: 1.27 lbs. (0.58 kg) Black Powder and TNT
AP: 0.3 lbs. (0.14 kg) Explosive D |
| Projectile Length | AP: 12.16 in (30.9 cm)
Common: 12.13 in (30.8 cm) |
| Propellant Charge 1 | Prior to World War I: 2.7 lbs. (1.2 kg) SPD
During World War II: 3.7 lbs. (1.68 kg) SPD or SPDN |
| Muzzle Velocity | 2,700 fps (823 mps) 2 |
| Working Pressure | 17.0 tons/in2 (2,680 kg/cm2) |
| Approximate Barrel Life | 4,300 rounds |
| Ammunition stowage per gun | Connecticut: 300 rounds
Mississippi: 250 rounds South Carolina: 300 rounds Others: N/A |
- ^Some SPD and SPDN cartridges had flashless pellets added which gave them a "reduced" flash.
- ^During World War II some of the older Mark 2 guns were considered constructionally weak and as a result had their working pressures derated down to 13.0 tons/in2 (2,050 kg/cm2) which reduced their muzzle velocities down to 2,100 fps (640 mps).
| Elevation | Muzzle Velocity | Distance | Striking Velocity | Angle of Fall | Flight Time |
|---|---|---|---|---|---|
| 2.0 degrees | 2,700 fps (823 mps) | 3,000 yards (2,740 m) | 1,230 fps (375 mps) | 3.4 | 5.1 seconds |
| 4.3 degrees | 4,500 yards (4,150 m) | 971 fps (296 mps) | 8.4 | 9.3 seconds | |
| 43 degrees | 14,600 yards (13,350 m) | --- | --- | --- | |
| AA Ceiling | 30,400 feet (9,270 m) | --- | --- | --- |
| Elevation | Muzzle Velocity | Distance | |
|---|---|---|---|
| 15 degrees | 2,100 fps (640 mps) | 7,000 yards (6,400 m) |
| Designation | Pedestal Mounts: Marks 2, 4, 5 and 7
AA Mount: Mark 11 1a |
|---|---|
| Weight | 3.0 to 4.2 tons (3.1 to 4.3 mt) |
| Elevation | Marks 2, 4, 5 and 7: -10 / +15 degrees
Mark 11: -10 / +85 degrees |
| Elevation Rate | Manually operated, only |
| Train | 360 degrees |
| Train Rate | Manually operated, only |
| Gun recoil | Mark 4: 8 in (20.3 cm)
Mark 5: 9.25 in (23.5 cm) Mark 7: 16 in (40.6 cm) Mark 11: 12 in (30.5 cm) |
- ^The Mark 11 was the first 3" (7.62 cm) AA mounting in the USN. This had a trunnion height of 66.25 inches (168.3 cm) compared to a height of 45 inches (114.3 cm) for the SP pedestal mountings.
"Naval Weapons of World War Two" by John Campbell
"US Battleships: An Illustrated Design History", "US Submarines Through 1945: An Illustrated Design History", and "US Naval Weapons" all by Norman Friedman
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"Navy Ordnance Activities: World War 1917-1918" by Navy Dept, United States, Bureau of Ordnance
"Range and Ballistic Tables 1935" by U.S. Department of Ordnance and Gunnery
31 May 2008 - Benchmark
12 February 2012 - Updated to latest template
03 April 2020 - Updated to HTML 5 format
23 October 2021 - Added mounting sketch