Ten Years to Doomsday by Chester Anderson & Michael Kurland (1964)
Chester Anderson (1932-1991), who leads the by-line on this science fiction novel, was a beatnik poet, musician, and rock and roll and underground journalist back in the days when this was a thing. He published two books of poetry and one novel before turning to science fiction with Ten
Years to Doomsday. His only other science fiction novel, The Butterfly Kid (1967), was the first novel in the Greenwich Village Trilogy and was nominated for a Hugo Award s Best Novel in 1968. [The three books in The Greenwich Village Trilogy was written by different authors; the second book (The Unicorn Girl, 1969) was by Kurland and the third (The Probability Pad, 1970) was by magician and mentalist T. A. Waters (1938-1998). The entire trilogy is a delightful counter-cultural romp and is recommended.]
Michael Kurland (b. 1938) is the better-known collaborator of Ten Years to Doomsday, which was his first novel. He has gone on to become a reliable and entertaining author in bothe the mystery and science fiction fields, sometimes combining the two as he did in two novels that continued Randall Garrett's Lord Darcy series which combined detection and wa world where magic works. Among other works, Kurland has written five novels about Sherlock Holmes' nemesis Professor Moriarty, five non-fiction books about crime and forensics, and edited three Sherlock Holmes anthologies, as well as editing and revising several of H. Beam Piper's short stories to form a science fiction novel.
Ten Years to Doomsday takes place millennia from today. The Terran Federation (so named because it started on Terra, although a number of non-human [and never seen] alien races are members) hase enjoyed two thousand years of peace. Then ships started vanishing near the galaxy's edge with no indication of what went wrong. None of the 24 ships that vanished had military weapons. A twenty-fifth ship, the Terran Beaver, happened to be a light cruise of the Terran Navy. An alien ship of unknown origins appears and fires at the Beaver, which responds and destroys the attacker.
Because details do not matter, we learn (don't ask how) that the attacking ship was a scout for an invading force from outside the galaxy and these invaders are capable of destroying the entire Federation. We also learn that the first probable stop for the invaders was the backward planet if Lyff, inhabited by a medieval society of peasants and tokenly ruled by a king although the real power lies in the global religion honoring "The Mother." Again don't ask how we know, but the invaders appear to be about tens years away from reaching Lyff. Political concerns on Terra make it impossible for the Federation to broach Lyff and protect it from the invaders. (For the sake of convenience, the authors call them the Migrants, who are "so nonhumanoid that, though thoroughly materia, they could only be described in mathematical equations.") The Migrants are -- like the boll weevil -- just looking for a home and anything that doesn't look like a home is completely destroyed because...well, that's just what they do.
Terra's problem then is to prepare Lyff for the looming invasion without the Lyffians knowing it. In other words, Terra has maybe ten years to surreptitiously bring from a medieval society to a space travelling society. So Terra sends three men from the top secret Special Detail L-2 to Lyff with orders to do exactly that. Working with the undercover Terran agent that had been stationed on Lyff and with a local poet-pickpocket, they begin by inventing the telegraph. Unintended consequences of doing this help further the planet's progress.
Lyffians, because they are working from a blank slate, are able to advance their sciences in ways that completely baffle the Terran team. They are super-smart and soon surpass the Terrans' carefully considered plans. On the political front a number of factions are secretly vying for control of the planet, including the government, a secret cabal, and a semi-secret and rather small revolutionary force. As these groups grapple with each other, and as the planet makes huge strides moving forward, the Migrants arrive with their destroying forces three years ahead of the projected time.
Even if the Migrants are defeated, behind the scenes there is even a bigger threat to the Terran Federation.
Ten Years to Doomsday is a fast-moving, explanation-eschewing, light adventure tale that is heavy on satire. There's is nothing deep or well worked out here. Nor should there be. Take it as it is -- a bit of fluff that will allow you several hours of reading pleasure.