Re: How were exploding cannonballs detonated?

Yes, indeed there were exploding cannonballs! Although some cannonballs 
were heated to red heat to cause fires when they landed (for example, in 
an enemy ship's sails).

Truely exploding cannonballs were hollow.  They were filled with black 
powder through a hole usually about an inch in diameter.  The hole was 
filled with a plug with a hole through it.  The plug was recessed into the 
cannonball shell (not sticking out as often shown in cartoons).  Through 
the hole was passed a short wick - usually a short piece of rope soaked in 
some cumbustible material.  The entire plug/wick apparatus was called a 
fuse.

After the cannon was packed with powder and tamped, etc., the cannonball 
wick was lighted and quickly dropped into the cannon - which was then 
fired quickly.  The wick was designed so that there was enough time to get 
it into the cannon, get the cannon fired, and still have enough time left 
to get to the enemy before it exploded. Obviously, this was a pretty 
important thing to get right (don't want the cannonball going off in your 
hand or in your cannon).  A specialist, called a fusileer, was in charge 
of figuring out the right type of fuse and length of wick to install for 
hitting certain kinds of targets.

Modern fuses are much more sophisticated.  They can be denoted by time, 
GPS position, radar-wave reflections, magnetic signatures, etc.  They can 
be set either before they are fired or set by radio or magnetic as the 
projectile shoots out the gun barrel at 2000 ft/sec!