The Catapult Trireme is not an upgrade of the Trireme. It is a separate vessel with fewer hit points and a slower fire rate than a Trireme but it has much more attack strength, range, and is armed with a Catapult, which can fire at a location instead of at a particular unit. The Catapult Trireme can be upgraded to the Juggernaught.War vessels fire at enemy villagers, military units, and boats within range.
Researching Alchemy increases attack strength. Ballistics increases accuracy. Engineering increases range.