Military Wiki
BL 7.5-inch naval howitzer
7.5 inch Naval Howitzer WWI AWM P01535.004.jpeg
On SS Boonah
Type Anti-submarine mortar
Place of origin  United Kingdom
Service history
In service 1917 - 192?
Used by British Empire
Wars World War I
Weight Gun & breech 812 pounds (368 kg)[1]
Barrel length Bore 63.75 inches (1.619 m)[1]

Shell HE 100 pounds (45.4 kg)
Calibre 7.5-inch (191 mm)
Breech single-motion interrupted screw
Muzzle velocity 480 feet per second (146 m/s)
Maximum range 2,100 yards (1,920 m)
Filling TNT
Filling weight 43 pounds (19.5 kg)[2]

The BL 7.5-inch howitzer (naval) was a British anti-submarine mortar developed during World War I.


The weapon was developed together with other similar devices early in 1917 and went into service in June 1917 in response to German unrestricted submarine warfare. It was mounted on merchant ships and patrol vessels. By 10 December that year, 377 were in service.[3]

The shell was fired at the submarine either on the surface or submerged - hence it had attributes of both armour-piercing shell and depth charge. It was designed to first penetrate the submarine's outer hull without breaking up, and then detonate against the inner hull after a 2-second delay,[1] destroying the submarine.

Writing a few years after the gun had gone into service, Admiral Jellicoe commented: "This weapon, although not very popular at first, soon, however, proved its value, when employed both from patrol craft and from merchant ships."[3]

Two were mounted on HMS Vindictive and used to bombard German defences during her participation in the Zeebrugge raid of 23 April 1918.


  1. 1.0 1.1 1.2 Hogg and Thurston 1972, Pages 148-149
  2. Standard shell was 100 lb, containing 43 lb TNT. In early 1918 a 500 lb stick bomb containing 250 lb TNT was developed, with a range of 300 yards. Hogg & Thurston 1972, page 148
  3. 3.0 3.1 Jellicoe, 1920. Chapter III


External links

This page uses Creative Commons Licensed content from Wikipedia (view authors).