Fred Karno’s army, n. — Green’s Dictionary of Slang

Fred Karno’s army n.

also Fred Karno’s mob

[the popular comedian Fred Karno (1866–1941), who fronted a series of slapstick mini-shows, often burlesquing music-hall. Orig. milit. use in WWI for the ‘New’, i.e. conscripted, army and in WWII for any platoon or section seen as inept]

a group of people considered incompetent.

1914–18		‘Fred Karno’s Army’ 🎵 We are Fred Karno’s Army / The ragtime infantry: / We cannot fight, we cannot shoot [etc.].
1939		V. Davis Gentlemen of the Broad Arrows 147: There goes Fred Karno’s army / What . . . use are they, etc.
1955		P. Larkin letter 31 May in Thwaite Sel. Letters (1992) 243: The Library they are planning looks at present like a rejected design for a cinema: if it is put up, it will be the laughing-stock of the British Isles [...] Fred Karno’s library.
1959		W. Hall Long and the Short and the Tall Act I: Fred Karno’s mob. That’s what you are, Fred Karno’s mob.