Earth's Last Citadel — Henry Kuttner

Four WWII combatants travel to a distant and dangerous future in this novel by “two of the most revered names from [science fiction's] Golden Age” (SFReviews.net).
 
During World War II, four bitter enemies are pulled forward a billion years in time by a master being from an alien galaxy. They arrive on a dying Earth -- to Carcasilla, Earth's last citadel -- where the mutated remnants of humanity are making their final stand against the monstrous creations of a fading world.
 
Thrust in the middle of this desperate struggle for survival, the last humans must put aside their differences and stop the looming Armageddon.
 
Praise for Henry Kuttner
“One of the all-time major names in science fiction.” -- The New York Times
 
“A neglected master.” -- Ray Bradbury, author of Fahrenheit 451
 
“Kuttner is magic.” -- Joe R. Lansdale, author of The Thicket