Vehicles also often fight in one-on-one duels and, as in animals, this can trigger an arms race. Above: The addition of a battering ram precipitated explosive growth in ship size in oared galleys of the ancient Mediterranean, settling in the end on the “five.” Below: Side-mounted cannons had the same effect on sailing galleons.

Emlen, Douglas J, Animal Weapons_ The Evoluti…, loc. 962