Green’s Dictionary of Slang

(US) a soldier, an infantryman; also attrib.

1937		in Our Army Jan. 20: The lousiest G.I. mule ever foisted upon defenceless doggies.
1952		(con. 1948) G. Mandel Flee the Angry Strangers 177: I was with some doggies in an English pub when the news broke.
1964		H. Selby Jr Last Exit to Brooklyn 11: Once in a while a doggie or seaman came in for a hamburger.
1971		Army Reporter Feb. in Maledicta VI:1+2 251: As our story begins, Little Red Riding Hood is leaving her hooch in the vil with a doggie pack of chop.
1987		(con. 1967) E. Spencer Welcome to Vietnam (1989) 45: The helmets of Marines and the helmets of doggies (the U.S. Army) are different.
1993		T. Jones Pugilist at Rest 11: Those doggies ain’t got jack.
2021		T. Pluck Boy from County Hell 63: He and two doggies had gone off base to see what they could see.