pom-pom
Concise Oxford English Dictionary © 2008 Oxford University Press:
pom-pom/ˈpɒmpɒm/
▶noun Brit. an automatic quick-firing two-pounder cannon of the Second World War period, typically mounted on a ship and used against aircraft.
– origin C19: imitative of the sound of the discharge.
'pom-pom' also found in these Oxford entries:

