Green’s Dictionary of Slang

the British army.

1956		J. Curtis Look Long Upon a Monkey 82: We’ll take it turn and turn about to kip, with one of us awake, just like doing stag in the kate.
1975		‘P.B. Yuill’ Hazell and the Three-card Trick (1977) 124: You niver went near the fakkin kate in the war, yah berk.