Green’s Dictionary of Slang

(Aus.) a British soldier.

1915		C.E.W. Bean Anzac Book 31/1: ‘Aw, yes,’ replies Tommy Atkins, or ‘Kitch,’ as he is beginning to be called. [...] And while the other is pulling at his fag: ‘Have you got any baadges, choom?’.
1921		N&Q 12 Ser. IX 344: Kitch. A man who enlisted in Lord Kitchener’s new Army.