British
Army acronym describing urban warfare, it stands for Fighting In Someone's House & Causing Havoc In People's Streets. It probably comes from some squaddie saying that urban warfare was fighting in someone’s house, another realised that it spelled “
FISH”. The logical
thing, given the British soldiers’ sense of humour would be to
add “& CHIPS” and find something appropriate to match the letters. Strictly speaking that makes it a bacronym, but a remarkably appropriate one for all that.