Green’s Dictionary of Slang

let her go (Gallagher)! excl.

(Aus./US) go ahead!

1887		Ft Worth Dly Gaz. (TX) 29 Aug. 6/4: Tom [...] sang out ‘Let ’er go, Gallagher’.
1888		Motherwell Times 27 Oct. 4/3: That boy of ours is chuck full of slang [...] he talks about me as the guv’nor, and this morning i heard him tell Bridget, ‘Let her go, Gallagher’.
1888		Waco Eve. News(TX) 21 July 2/1: Allen [...] walked the scaffold with a firm tread [...] and shouting ‘Let her go Gallagher’ was launched into the great beyond.
1893		W.S. Walsh Literary Curiosities 403: Gallagher. Let her go, Gallagher! a humorous Americanism, meaning ‘All right! Go ahead!’.
1895		Truth (Sydney) 27 Jan. 1/7: Once a woman has set her soul; on sin, it’s a case of ‘Let her go, Gallagher,’ and nothing [...] can stop her.
1897		Coventry Eve. News 9 Aug. 4/1: A Dane [...] was hanged at Tucson, Arizona. He [...] danced a jog and said ‘Let her go, Gallagher’.
1897		Progress (Shreveport, LA) 30 Jan. 2/1: Wester Shreveport is just a booming. Let her go Gallagher!
1901		Bulletin (Sydney) 14 Dec. 12/3: In future every pastor, ere holding forth, should take a vote of his audience as to whether her should ‘Shut Up,’ or ‘Let Her Go, Gallagher.’.
1905		R.F. Outcault ‘Buster Brown’ [comic strip] Let her go, Gallagher.
1910		O. Johnson Varmint 135: ‘All ready?’ ‘Let her go!’.
1914		Bulletin (Sydney) 19 Nov. 11/1: A German spy was shot and buried there last week. He refused to be blindfolded, and simply sat in a chair and said (in effect) ‘Let her go, Gallagher.’ And Gallagher did.
1927		Nottingham Eve. Post 5 Nov. 5/6: The forthcoming film, entitled ‘Let her go, Gallagher’.
1929		M. Levin Reporter 7: Hit ’er up, old man; Parksite hotel. Newspaper stuff so let ’er go.
1939		K. Tennant Foveaux 212: ‘Right-o,’ Tommy would roar, as he heaved a stout lady and her children on board. ‘Let her go’. And he shrilled his whistle as they lurched away.
1943		J.A.W. Bennett ‘English as it is Spoken in N.Z.’ in AS XVIII:2 Apr. 91: The American tag ‘Let her go, Gallagher,’ described by Mencken as ‘a shortlived, silly phrase,’ can still be heard in New Zealand; it presumably goes back to comedians’ patter.
1994		F. Mac Anna Ship Inspector 95: All right, let her go.