The QF 4-inch gun Mks I, II, III were early British QF (quick-firing) naval guns originating in 1895. They all had barrels of 40 calibres length.

Naval service

The gun was intended to be a more powerful alternative to the quick-firing 3-inch QF 12-pounder gun, and a faster-firing replacement for the BL 4-inch gun. It was mounted on the following ships : Its 25 lb shell proved insufficiently powerful to make it much of an improvement on the 12-pounder. From 1907 onwards it was succeeded in its class on new warships by the BL 4 inch gun Mk VIII, which fired a 31 lb shell.

Coast Defence gun

From 1906 a number of Mk III guns were transferred from the Royal Navy for use as coast defence guns around the United Kingdom, and remained until 1939. In 1918 three guns were in service at Dover Garrison and eight at Forth Garrison.

World War I land service

On 20 September 1914 the British cruiser HMS Pegasus (1897) was sunk by SMS Königsberg (1905) in Zanzibar harbour. Her 8 QF 4-inch Mk III guns were recovered and used ashore in the East African campaign. Some were used as coast defence guns at Zanzibar and Mombasa. Two guns, and from 11 February 1916, three guns, were used by 10th Heavy Battery manned by the Royal Marines, mounted on improvised field carriages and towed by Packard lorries, supported by six REO lorries carrying ammunition.

Surviving guns