Early 20th century; earliest use found in War Illustrated. From O + pip (name for the letter ‘P’ in the services' phonetic alphabet), as abbreviation for observation post.
Definition of O. Pip in US English:
O. Pip
noun
military slang
An observation post.
Origin
Early 20th century; earliest use found in War Illustrated. From O + pip (name for the letter ‘P’ in the services' phonetic alphabet), as abbreviation for observation post.