The story
From flat + top. Sense of “aircraft carrier” attributed to the message, “Scratch one flattop,” radioed during the Battle of the Coral Sea by LCDR Robert E. Dixon to the USS Lexington, whose commanding officer credited the pilot with coining the standard USN slang.
First known use, by meaning
- from 1942 An aircraft carrier.
Etymology from Wiktionary, CC BY-SA 4.0.