The High Crusade
In the year of grace 1345, as Sir Roger Baron de Tourneville is gathering an army to join King Edward III in the war against France, a most astonishing event occurs: a huge silver ship descends through the sky and lands in a pasture beside the little village of Ansby in northeastern Lincolnshire. The Wersgorix, whose scouting ship it is, are quite expert at taking over planets, and having determined from orbit that this one was suitable, they initiate standard world-conquering procedure. Ah, but this time it's no mere primitives the Wersgorix seek to enslave—they've launched their invasion against free Englishmen! In the end, only one alien is left alive—and Sir Roger's grand vision is born. He intends for the creature to fly the ship first to France to aid his King, then on to the Holy Land to vanquish the infidel. Unfortunately, he has not allowed for the treachery of the alien pilot, who instead takes the craft to his home planet, where, he thinks, these upstart barbarians will have no choice but to surrender. But that knavish alien little understands the indomitable will and clever resourcefulness of Englishmen, no matter how great the odds against them...
Alternative histories (Fiction), Military science fiction, Life on other planets, Fiction, Aliens
Poul Anderson
Poul William Anderson was an American science fiction author who began his career during one of the Golden Ages of the genre and continued to write and remain popular into the 21st century. Anderson also authored several works of fantasy, historical novels, and a prodigious number of short stories. He received numerous awards for his writing, including seven Hugo Awards and three Nebula Awards.

Anderson received a degree in physics from the University of Minnesota in 1948. He married Karen Kruse in 1953. They had one daughter, Astrid, who is married to science fiction author Greg Bear. Anderson was the sixth President of Science Fiction and Fantasy Writers of America, taking office in 1972. He was a member of the Swordsmen and Sorcerers' Guild of America, a loose-knit group of Heroic Fantasy authors founded in the 1960s, some of whose works were anthologized in Lin Carter's Flashing Swords! anthologies. He was a founding member of the Society for Creative Anachronism. Robert A. Heinlein dedicated his 1985 novel The Cat Who Walks Through Walls to Anderson and eight of the other members of the Citizens' Advisory Council on National Space Policy.

Poul Anderson died of cancer on July 31, 2001, after a month in the hospital. Several of his novels were published posthumously.

Source: Goodreads