The Mark 1 was a simply constructed weapon used as a boat gun. Monobloc construction with a Fletcher breech mechanism and used a hydraulic recoil piston screwed directly onto the gun.

The Mark 1 Mod 1 was of similar construction but used a solid lug for the piston rod. The barrel slid in the cradle and had two keys on the horizontal line through its center. Used a modified Fletcher breech mechanism.

Gun Characteristics

Designation 3"/21 (7.62 cm) Mark 1
Ship Class Used On N/A
Date Of Design About 1890
Date In Service About 1890
Gun Weight 384 lbs. (174 kg)
Gun Length 69.6 in (1.768 m)
Bore Length 64.3 in (1.633 m)
Rifling Length N/A
Grooves N/A
Lands N/A
Twist RH 1 in 29.89
Chamber Volume N/A
Rate Of Fire about 8 - 9 rounds per minute


Type Bag
Projectile Types and Weights HE: 13 lbs. (5.9 kg)
Bursting Charge N/A
Projectile Length N/A
Propellant Charge N/A
Muzzle Velocity 1,150 fps (351 mps)
Working Pressure 9.5 tons/in2 (1,500 kg/cm2)
Approximate Barrel Life N/A


Range with 13 lbs. (5.9 kg) Shell
Elevation Range
19.5 degrees 5,000 yards (4,570 m)

Mount/Turret Data

Simple carriage mounting. Maximum elevation was slightly greater than 19.5 degrees.


"US Naval Weapons" by Norman Friedman
"A Treatise on Rifling of Guns" by Carl F. Jeansén
"United States Naval Guns: Their Marks and Modifications" Ordnance Pamphlet No. 127, December 1916, Second Revision June 1924
Gene Slover's Navy Pages
Special help from Leo Fischer

Page History

03 December 2006 - Benchmark
07 August 2017 - Converted to HTML 5 format