QF 4 inch Mk V naval gun

The QF 4 inch Mk V gun was a Royal Navy gun of World War I which was adapted on HA mountings to the heavy anti-aircraft role both at sea and on land, and was also used as a coast defence gun.

Naval service
This QF gun was introduced to provide a higher rate of fire than the BL 4 inch Mk VII. It first appeared in 1914 as secondary armament on Arethusa class cruisers, was soon adapted to a high-angle anti-aircraft role. It was typically used on cruisers and heavier ships, although V and W class destroyers of 1917 also mounted the gun. Mk V was superseded by the QF 4 inch Mk XVI as the HA (i.e. anti-aircraft) gun on new warships in the 1930s, but it served on many ships such as destroyers and light cruisers in World War II.

Army anti-aircraft gun
Early in World War I several guns were supplied by the Navy for evaluation as anti-aircraft guns for the home defence of key installations in Britain. They were mounted on static platforms and proved fairly successful after a fixed round was developed to replace the original separate round, and more followed. The AA mounting allowed elevation to 80° but loading was not possible above 62°, which slowed the maximum rate of fire. At the Armistice a total of 24 guns were employed in AA defences in Britain and 2 in France. After World War I the guns were returned to the Navy.

Coast Defence gun
From 1915 to 1928 several guns were mounted in forts to guard the estuary of the River Humber. 

Anti-aircraft performance
The following table compares the gun's performance with the other British World War I anti-aircraft guns:-

Ammunition
Ammunition for the original low-angle guns introduced in World War I was Separate QF i.e. the shell and cartridge were separate items, but in World War II most guns used Fixed QF ammunition i.e. a single unit.

Weapons of comparable role, performance and era

 * 10.5 cm SK L/45 naval gun Approximate German equivalent firing slightly heavier shell

Surviving examples

 * A gun from HMNZS Tutira in front of the Devonport Naval Base, Auckland, New Zealand