Same thing happened to me.
Here was my defensive army:
M10 Tank Destroyer (R2) 1 / 5
Here was the offensive army:
M8 Greyhound (R2) 0 / 15
M8 Greyhound (R3) 0 / 1
You can't tell me 5 Tank Destroyers couldn't hit 16 apc's?! Heck, I'd be happy with hitting one of them.