BL 4-inch Mk VII naval gun

The BL 4-inch gun Mk VII was a British high-velocity naval gun introduced in 1908 as an anti-torpedo boat gun in large ships, and in the main armament of smaller ships. Of the 600 produced, 482 were still available in 1939 for use as coastal artillery and as a defensive weapon on Defensively Equipped Merchant Ships (DEMS) during the Second World War.

Naval history
The guns armed the following warships :
 * Bellerophon-class battleships, laid down 1906
 * St. Vincent-class battleships, laid down 1907
 * Boadicea-class cruiser scout cruisers, laid down 1907
 * HMS Neptune (1909), laid down 1909
 * Colossus-class battleship (1910) battleships, laid down 1909
 * Indefatigable-class battlecruisers, laid down 1909
 * Orion-class battleships, laid down 1909
 * Lion-class battlecruisers, laid down 1909
 * Bristol-class light cruisers, laid down 1909
 * Blonde-class cruiser scout cruisers, laid down 1909
 * Active-class cruiser scout cruisers, laid down 1910
 * King George V-class battleship (1911) battleships, laid down 1911

The gun was succeeded in the "heavy" 4-inch class on new warships commissioned from 1914 onwards by the QF 4-inch Mk V. This new generation of warships were more heavily armed, and the BL Mk VII's role as secondary armament on capital ships and primary armament on cruisers was taken over by the BL 6-inch Mk VII and BL 6-inch Mk XII while the 4-inch calibre became the secondary armament on cruisers and primary armament on destroyers.

In World War II many guns were used to arm merchant ships.

World War I field gun service
A battery of 4 guns mounted on field carriages was first deployed with the South African Heavy Artillery in the German South West Africa campaign in 1915 and returned to England in September. They were then deployed in the East African Campaign from February 1916 with 11th Heavy Battery (renumbered 15th Battery from April 1916) manned by the Royal Marine Artillery.

Surviving examples

 * 2 Mk VII guns from HMS New Zealand outside the Auckland War Memorial Museum

Weapons of comparable role, performance and era

 * 4"/50 caliber gun US equivalent