The Trireme has more hit points, attack strength, and range than a War Galley. The Trireme cannot be upgraded. However, you can research the Catapult Trireme, which is stronger than the Trireme.War vessels fire at enemy villagers, military units, and boats within range.
Researching Alchemy increases attack strength. Ballistics increases accuracy. Woodworking, Artisanship, and Craftsmanship increase range.