Green’s Dictionary of Slang

bully n.2

[Fr. boeuf boulli, boiled beef]

bully beef (pickled or tinned beef).

[[UK] ‘The Stage-Coachman Abroad’ in Bentley’s Misc. IV 605: Then came in a large white dish with little square slices of b’iled beef, as Jack said was ‘bully’ [...] If Dutch courage means a glass of gin, Belgian bully means beef with the strength b’iled out on it].
[UK]Grey Brigade 11 Dec. 3/3: Cold is my dug-out, damp my feet, / Nothing but biscuits and bully to eat.
[Aus](con. WWI) A.G. Pretty Gloss. of Sl. [...] in the A.I.F. 1921–1924 (rev. t/s) n.p.: bully. Abbreviation of Bully Beef. A name given to the preserved meat issued, usually in one pound tins.
[Aus]L. Glassop We Were the Rats x: It’s practically all bully beef and biscuits here, George. No matter how cleverly the cook disguises the old bully, we always see through it.
[NZ](con. 1940s) G. Slatter Gun in My Hand 184: Don’t choke on the bully we said.
[Aus](con. 1941) R. Beilby Gunner 16: Several tins of precious bully.
[NZ]J. Henderson Exiles of Asbestos Cottage 98: Sometimes he’d take a dozen tins of bully.