AMTRAC

Set to 2 different clues across 2 published puzzles, most often “Amphibious W.W. II vehicle” — The New York Times, Saturday, 26 February 2011.

6 letters

Every clue on record, most used first

Amphibious W.W. II vehicleonce
The New York Times — Saturday, 26 February 2011
Military vehicle for landing assault troopsonce
The New York Times — Monday, 10 July 2000