"Strike Witches" isn't by any means anything new in the anime scene, but it is certainly a mind blowing puree of ideas. Once again, the Japanese have gone that extra step into bizarro land and we can all enjoy it.
Firstly, this belongs in the fascinating sub-sub genere of "What we really did during the War." See WWII is cool. Great battles, neat planes. All the things that just ping onto an otaku's heart. Trouble is, they were on the wrong side. So they just can't gleefully play Japanese fascists with guns. So there has been this genre which is generally described as "Well, yes there were bad japanese folks but the real Japan was fighting... ALIENS!" In "Strike Witches," it goes the extra step of creating an alternate world. In this world in 1939 nasty aliens that look like big bombers have invaded the world. They are nigh impregnable, and pack a lot of energy weapons.
Oh who can stop them? Why witches of course. See there are witches in this world and it seems to be a generally known fact. So far, all the witches I've seen are pretty young girls. They must be keeping the hags and boys some where else. So now we got a little Harry (Harriet) Potter in WWII action, but see the witches aren't strong enough so they need something else.
Well, that something else are these THINGS. Think about someone telling a metal worker what a panty hose is and then that metal worker comes up with his interpetation of that. Now add a couple of tiny wings on the bottom and PROPS. Yes, a pair of spinning blades. Ladies don't cross your legs!
How does this work? Oh easy enough. The witch (who is always wearing short shorts of course, what isn't explained is why the camera must be a dwarf given camera placement) slips her dainty legs into the tubes and then there is a rush of magic. Suddenly she gets cutesy ears and maybe an oh so cute little tail. She then grabs a REALLY BIG GUN, and flies up to kick alien butt.
Our story follows plucky young Japanese witch. She has an affinity for healing power and tends toward pacifism. She's contacted by the eye patch wearing leader of the Strike Witch to join up, but she's not interested. She becomes interested when she learns her lost daddy help built the leg THINGS that the strike witches use. So now she's the newbie of an elite squad of giggling girls in short shorts and REALLY BIG GUNS. Somewhere an Otaku has died and gone to heaven.