In the late 1960s when, as a somewhat lazy student, I read more fiction (nearly all SF) than ever before or since, Harry Harrison was one of my favourite authors. He wrote short, fast-paced and often hilarious page-turners, and I still have a few of his classic novels on my shelf: Bill the Galactic Hero (a spoof of Heinlein's Starship Troopers) and the Deathworld trilogy. Probably his best-known comic character was Slippery Jim DiGriz of The Stainless Steel Rat series, but he also wrote more serious fiction, most famously Make Room! Make Room! about overpopulation. Although he was still publishing novels in the 1990s (and has a new Stainless Steel Rat one due out this year) I last read his work in the early 1970s, with A Transatlantic Tunnel, Hurrah! (also published as A Tunnel Through the Deeps), a very tongue-in-cheek take on an alternative Victorian world which would nowadays automatically be classified as "steampunk". I'm not quite sure why I bought A Rebel in Time (published 1983) but it's been sitting on my shelf for a while and I felt like some light reading (Iain M. Banks tends to do that to me) so I picked it up. It was not quite what I expected.
A Rebel in Time deals with two familiar SF themes; time travel and alternate histories. A present-day soldier, Troy Harmon, is recruited into an obscure government organisation whose job is to "watch the watchers"; to keep an eye on people with high security clearance. He starts to look into the puzzle of Colonel McCulloch, head of security at a top-secret research establishment, who has been behaving strangely - in particular, he's been converting most of his assets into gold. Almost half of the novel is concerned with Harmon's investigation, always one step behind McCulloch, while he tries to understand what's happening - until McCulloch suddenly disappears, leaving a trail of crimes behind him. Harmon gradually pieces together what has happened, and realises that McCulloch has used the time-travel experiments of the research establishment to send himself into the past, just before the American Civil War, together with a fortune in gold and with plans for making the very simple Sten sub-machine gun. Harmon realises that McCulloch, a pathological racist, is going to try to help the Confederacy win the war. He decides that he must follow him on a one-way trip into the past to try to prevent this from happening, since he has a powerful motive: Harmon is black.
This is a serious novel a lot longer and more deliberately-paced than his typical 1960s work (although at just over 300 pages, still not long by current standards), but the Harrison story-telling skills are as strong as ever and it is a gripping page-turner. Harmon's experiences in the slave culture of the southern USA in the late 1850s ring true, and the ending, while certainly not of the "happily ever after, all tied up" type is exactly right.
I did have one technical issue over the Sten gun. I have no doubt that the gun itself - possibly the simplest and crudest 20th century firearm to have seen general service - could have been manufactured in the 1850s, but I have serious doubts about the ammunition. Possibly the drawn brass cases might have been, although I'm not sure (coiled brass sheets were used when cartridges were first developed) but the propellant is another matter. The Sten's 9x19 Parabellum ammunition was designed for smokeless powder, much cleaner burning and more efficient (requiring less volume) than the gunpowder in use in the 1850s; the advances in chemistry which made this possible didn't happen until the 1880s. Loaded with gunpowder, the ammunition would have been much less powerful, and even if it could be made to work it is likely that the gun would have become quickly fouled by gunpowder residues, causing it to jam.
Despite this nerdish niggle A Rebel in Time is a very impressive and enjoyable story.
If this plot sounds vaguely familiar you might be thinking of Harry Turtledove's The Guns of the South, which also features people from the present day taking modern automatic guns back to the American Civil War to help the Confederacy win. This was published nine years after A Rebel in Time and has also been sitting unread on my shelf for a very long time, so I'll tackle that soon to compare and contrast.