Concerning Mumakil...
Burning pigs! How nasty - I'd forgotten that one, not sure I'm too happy to be reminded.
For me, the film Mumakil were far bigger than I'd imagined, something not more than twice the size of an ordinary elephant would have appeared more believable.
I think that in ancient times the elephants had greatest effect on troops who hadn't encountered them before, once trained in how to deal with the beasts, they could often become a big liability to the elephant-using side.
This put me in mind of an old thread
Elephants Oliphants
They were also used as command platforms by generals, especialy in India, I guess that you'd get a good view from the top of a Nelly and, as long as you stayed well behind the front line, you'd hope that it wouldn't go bonkers. They're still used in National Parks as tiger-spoting platforms, with the added bonus that the tiger is unlikley to eat you as long as you stay on the howdah. A good elephant is also a great substitute for a JCB, just this year I saw some on TV helping shift the debris from the terrible tsunami disaster. Apparently the elephant driver (mahout) has a really close relationship with the elephant, as they have likely trained and worked together for many years. therefore, in a battle situation, the mahout may well be reluctant to put his friend (and himself!) in harm's way.
Hooray for peaceful elephants