If you look at the cap badge of the Grenadier Guards, it's a round thing with a flame coming out of the top. It's the same thing as the 18th c. shell: a hollow cast-iron ball stuffed with gunpowder and with a wooden plug fitted in the hole, and which contains the fuse. If fired from a gun, the gun's charge would light the fuse. I guess it was an anti-personnel thing, while the solid shot was meant to damage the ship.

Steve