Battle of Vukovar

[Anomalocaris]

They seem to contradict the second law of thermodynamics. It says that the efficiency of a heat engine must be less than 100%. In a bomb, you are supposed to put very little heat to activate it, yet get tremendous amount of mechanical energy and heat from it. Its efficiency as a heat engine would have to be much greater than 100%.

No, you are confusing the heat input with heat trigger.   The heat input into the bomb is the chemical energy stored in the explosive when the ingredients of the explosives were made and put together, not the heat of the fuse that served to trigger the release of the stored chemical energy from the explosive.  The total stored energy is greater than the sum of mechanical and heat energy released when you trigger it.

An analogy is a mouse trap.   The energy released when the trap snaps shut is much greater than the energy put in to trigger the trap.   When the mouse pulls on the cheese he certainly didn’t pull with enough energy to break his own neck and crush his own skull.  Where did the energy of the mouse trap that did this come from?  It came when you set the trap in the first place by winding the torsion spring.