Three Go Back is a novel by J. Leslie Mitchell (known by hi pseudonym Lewis Grassic Gibbon) published in 1932.
Three Go Back is a novel in which an airship goes back in time 25,000 years and the passengers encounter Cro-Magnons and Neanderthals.
Dave Langford reviewed Three Go Back for White Dwarf #79, and stated that "it's a pleasant novel, and reminds you that while American magazine heroes were zapping greenskins with their blasters, some 1930s authors still considered SF a literature of ideas."[1]