Strike Witches is a light novel and anime series set in an alternate World War II setting in which the nations of the world band together to defend against an alien invasion. Their only trump cards are witches (genderswapped versions of real life World War II fighter pilots) who don engine-shaped leggings known as striker units to fly and do battle in the sky.
The series later spawned several sequel and spin-off, which were later collectively named the World Witches Series.
*Written by Yamaguchi Noboru
*Illustrated by Shimada Fumikane, Ueda Hashigo
This tag implicates world_witches_series (learn more).