One of the mysteries of the English language finally explained.
An armed and camouflaged merchant vessel used as a decoy or to destroy submarines (chiefly in the First World War (1914–18).
Early 20th century; earliest use found in Army & Navy Gazette. Probably arbitrary (or perhaps from the initial letter of query), probably after slightly earlier use of P-boat for a patrol boat.
In this article we explore how to impress employers with a spot-on CV.