Green’s Dictionary of Slang

(US) World War II.

1961		(con. early 1950s) J. Peacock Valhalla 55: He was a prisoner of war during Big Two. [Ibid.] 60: Here were the offspring of those other mercenaries who had fought in Big Two who were the offspring of the mercenaries who fought in Big One.
1967		(con. 1951) McAleer & Dickson Unit Pride (1981) 24: Nine weeks on the Anzio beachhead in the Big Two.
1995		R. Campbell Wizard of La-La Land (1999) 16: The Big Two had been Rialto’s war and Canaan’s war. Vietnam had been Bosco Silverlake’s war.
2004		P. Heller at www.hellermountain.com 7 Dec. 🌐 Therefore, in about six months, the war on terror will have passed Big Two to become the second-longest military engagement in the history of a nation that was birthed in combat.