Brian-
See http://www.halfbakery.com/idea/Trained_20bat_20bombs for one of many pages on the web that discusses them.
On that same page, this entry caught my eye:
"Probably we'd end up with the same problem as the Russians who tried to train dogs to run under tanks in world war 2, with the intention of strapping explosives to them and setting them out against German tanks. Problem was, the dogs had been trained under diesel Russian tanks which smelt very different to petrol/gasoline-powered German tanks, and therefore they ran under the wrong tanks.

I also found in the same webpage (see link) a biblical reference to Samson setting fire to foxes' tails and letting them run into his enemies' fields."

Kinda puts the issue of what might be used by terrorists to deliver a destructive payload in perspective: anything that moves has the potential
What the heck is special about a model airplane?

Abel