The Pom Pom is also a World War II-era nickname for a then-common type of anti-aircraft automatic gun, manufactured by Vickers. It was deployed in huge numbers aboard ships in the Allied navies, as it was relatively powerful, could be mounted anywhere there was a flat deck spot, and only took a maximum of two crewmen to operate (although one could do so in a pinch, loading for himself).

The pompom (or pom-pom, pom pom, etc.) was a 40.5mm automatic cannon that fired 2-lb. (2pdr) ammunition. It was essentially a last-ditch anti-aircraft tactic - these were cheap and plentiful, so when under attack, a ship or convoy could throw enormous amounts of metal into the air at (one hopes) the attacking aircraft (see Big Sky Theory of Navigation and Golden BB).

'Pom-pom', no doubt, refers to the noise made by the weapon. Due to its larger shot, and heavy construction, the gun did not cycle fast enough to make the 'chattering' or rattling noise associated with automatic weapons. Instead, each of the powerful (for a gun) shells would be heard in sequence, with a continuous series of reports: pom-pom-pom-pom.

This weapon was first manufactured by the Maxim-Nordenfelt Gun and Ammunition company (I believe) in Crayford, England in 1888. Naturally, it wasn't used against aircraft originally; rather, the bursting shells were seen as highly effective against massed troops or cavalry.

There remains, to this day, a pub near where the factory used to lie, named after it (the Nordenfelt) and nicknamed after it as well (the pompom). Eventually, this firm changed monikers to Vickers, Sons and Maxim Ltd. Under the name 'Vickers', it continues to manufacture arms up to today, selling them to the British government and approved end-users. The company has moved up from the little 2pdr pompom, though; it now makes aircraft, submarines, ships, armored vehicles, and, of course, heavy firearms.