The 8"/23 (20.3 cm) Mark 7 was an ASW Howitzer that could be used in place of the standard 4"/50 (10.2 cm) destroyer gun. Besides destroyers, it was planned to mount these on battleships, cruisers and gunboats. Following tests with two British 7.5" Howitzers on USS Caldwell (D-69), the Navy planned to mount two of the new 8" (20.3 cm) Howitzer on destroyers, but none were actually installed. Orders were placed for 89 guns with the first one being test fired in Februay 1918, but it is not certain how many were actually completed. None survived to World War II.

Manufactured from a single alloy-steel forging.

The USN 8"/15 (20.3 cm) Mark 8 was the Vickers 8" (20.3 cm) BL Mark 6 Model 1917 land howitzer that was issued to the US Marine Corps during World War I. Weight with breech block was 6,552 lbs. (2,972 kg).

The data that follows is for the Mark 7 unless otherwise noted.

Gun Characteristics

Designation 8"/23 (20.3 cm) Mark 7
Ship Class Used On Planned for Flush-deck destroyers of World War I
Date Of Design 1917
Date In Service 1918
Gun Weight 5,560 lbs. (2,522 kg) with breech block
Gun Length oa 190 in (4.826 m)
Bore Length 182.9 in (4.646 m)
Rifling Length 156.8 in (3.983 m)
Grooves (48) 0.050 in (1.27 mm) deep
Lands N/A
Twist Increasing RH 1/40 to 1/15 at 115 in (2.921 m) from origin
Chamber Volume 1,300 in3 (21.3 dm3)
Rate Of Fire 3 - 4 rounds per minute


Type Bag
Projectile Types and Weights ASW Mark XII Mod 4 - 285.3 lbs. (129.4 kg)
Bursting Charge 70 lbs. (31.8 kg)
Projectile Length 43.25 in (109.9 cm)
Propellant Charge 5.5 lbs. (2.5 kg) SP
Muzzle Velocity 700 fps (213 mps)
Working Pressure N/A
Approximate Barrel Life N/A
Ammunition stowage per gun N/A

The original HE projectile for this weapon was a special flat-nose ASW type. This weapon may have later used the standard 8" (20.3 cm) 260 lbs. (118 kg) projectile.


Ranges of HE ASW projectiles
Elevation Range
20.8 degrees 2,600 yards (2,380 m)

Mount/Turret Data

Designation N/A
Weight N/A
Elevation N/A
Elevation Rate Manual operation, only
Train about +150 / -150 degrees
Train Rate Manual operation, only
Gun recoil N/A
Loading angle N/A

This mounting was designed to be interchangeable with the standard 4"/50 (10.2 cm) Mark 12 mounting used on the flush-deck destroyers of World War I.

Additional Pictures


"US Naval Weapons" and "US Naval Weapons of World War One" both 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
"Navy Ordnance Activities: World War, 1917-1918" by Navy Dept, United States, Bureau of Ordnance
Gene Slover's Navy Pages
Special help from Leo Fischer

Page History

31 May 2008 - Benchmark
07 February 2015 - Added data on gun and projectiles
29 July 2016 - Converted to HTML 5 format