yes...either from submarines or from the city/fort near where they will land. GM's only have a range of 4 (i think) so if you don't have a submarine fleet, you have to wait until they are practically in your waterways to use them.
I love to load them on subs to soften up the defending destroyers/battleships-then let my own subs, destroyers/battleships, & even transports finish them off.
