QF 4-inch naval gun Mk I – III

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 :
 * Pelorus-class cruiser third-class protected cruisers of 1896
 * Condor-class sloops of 1898
 * Cadmus-class sloops of 1900
 * Topaze-class cruiser third-class cruisers, launched in 1903
 * Invincible-class battlecruisers of 1906

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

 * A gun from HMS Pegasus used in the WWI land campaign stands outside Fort Jesus on Mombasa Island, Kenya, next to one of the 10.5-cm guns from SMS Königsberg (1905).
 * A gun from HMAS Protector (1884) is on display outside the Elizabeth and Salisbury Navy Club in Elizabeth, South Australia.
 * A gun was installed in 1918 on the island of Hirta in the St Kilda archipelago, northwest Scotland, after a German submarine attack there, by the German submarine SM U-90.