I had done this by accident, I had built all bombards, mortars, and Fire Lancers, I was donating to our bases during war. I forgot what I was doing and simply bitty retrain. So later, when I went to do a regular attack, I was cringing because I had 5 mortars, 4 bombards, a healing cart, and like 19 Fire Lancers. I wiped wiped out the enlightenment base that was easily10 levels higher than me at the time.
Grant you the base actually allowed me to use it's own walls against it and my mortars destroyed everything before troops ever got to them, but five of them plus the 2 I had donated to me, wad like watching fire works, they destroyed building before the bombards even lined up to shoot.