Prototype

This is easily done in an APC or tank. Find a road with a high concentration of civilians on both sides of the road. Start running over them on one side, and fire your cannon at the civilians at the other side of the road. The trophy should unlock without a problem. Alternatively, you could wait until you play one of the two kill events where you get a Thermobaric Tank (Rolling Thunder and Demolition) as it should be very easy to unlock this due to the large blast radius of the tank's primary weapon.