This trophy is from the Sands Of Africa DLC but you can also unlock it in the main game (if you have downloaded the DLC of course).
In the mission "Payback Time" in Act I, you start out with the objective to destroy a lot of ships in an enemy harbour. Use your rockets and bombs, and you should easily get this trophy (when playing on easy) without even trying that hard (I got the corresponding achievement without going for it, when playing this game on X360 I didn't even realise that the DLC achievements could already be unlocked at this time).
Note: It's also possible to get the 300% Accuracy trophy from the same DLC in this level.
The absolute first time in the campaign when you can get this is on the Act I level "The Battle of Midway". During this level, you have to sink four Japanese carriers. There's a fleet of smaller ships around the big carriers, and on easy these smaller ships go down with one hit of your secondary weapon (take note that it's torpedoes instead of regular bombs, so you have to let them go in the water and not on top of the ships). I got the trophy this way when playing on PS3, again without going for it.
If you're having trouble doing this trophy on "The Battle of Midway", don't try to restart the mission the whole time but just wait for the next mission. The next mission is "Payback Time", which I talked about at the start of this guide, and has a lot more ships that can be destroyed. This bit about "The Battle of Midway" is just for the people who have not gotten to "Payback Time" yet.