The term 'Nile Nippers' is a nickname for the Asps, a four-letter acronym for the Anti-Submarine Patrol and Escort Service. This service was established during World War II by the Royal Navy to protect merchant ships from German U-boats in the Mediterranean Sea. The nickname 'Nile Nippers' was given to the Asps due to their presence in the Mediterranean, which is connected to the Nile River.