This book sounds ridiculous, and a little awful, but I must convey to you how much fun I found this book to be.
The High Crusade is the chronicle of a Roger de Tourneville, as recorded by Brother Parvus and the events that took place after a spaceship landed near the town of Ansby, where Sir Roger was preparing to depart on a crusade. The aliens disembark their spaceship wielding a phase guns, but are quickly overtaken by an English heavy cavalry charge. Sir Roger intends to take the spaceship with him in his pursuit of war, but due to a traitorous alien, the entire English town end up on the alien planet. So the English crusade through the universe in the name of Christ our Lord.
It's awesome.