This was tested in the Arethusa-class light cruisers HMS Arethusa and Undaunted but did not enter full service, being replaced instead by a larger weapon, the QF 2-pdr Mark II (see below).

[5] Surviving weapons were brought out of storage to see service in World War II, mainly on board ships such as naval trawlers, motor boats and "armed yachts".

It was superseded in the 1930s as a primary AA weapon on Italian warships by more modern guns, such as the Cannone-Mitragliera da 37/54 (Breda).

Design work for such a weapon began in 1923 based on the earlier Mark II, undoubtedly to use the enormous stocks of 2-pounder ammunition left over from the First World War.

Lack of funding led to a convoluted and drawn-out design and trials history and it was not until 1930 that these weapons began to enter service.

[11] This large ammunition capacity (1,120 rounds) gave the eight-barrelled mount the ability to fire continuously for 73 seconds without reloading.

On the other hand, there was the distinct disadvantage that the gun was designed for cordite powder, and no manufacturing facilities for the production of this ammunition were available in the United States.

The success of the pompom in action was more than offset by the proved qualities of the Bofors in the hands of a number of powers who were using it, and the Bureau decided to join that group.

It was intended that the curtain of fire it threw up would be sufficient to deter attacking aircraft, which it did, but was hampered by the ineffective Mk III director.

[13] The MK IV Director with a Gyro Rate Unit and Type 282 radar[14] was a great advance and was introduced on the King George V-class battleships.

[20] The Royal Navy judged the pom-pom's effectiveness to range from about half that of the Bofors, per gun, against torpedo planes to about equal against Kamikaze attackers.

[21] It was a ubiquitous weapon that outnumbered the Bofors gun in Commonwealth naval service[22] up to the end of World War II and it shot down many Axis aircraft.

Later innovations such as Remote Power Control (RPC) coupled to a radar-equipped tachymetric (speed predicting) director increased the accuracy enormously and problems with the fuses and reliability were also remedied.