Once metal cladding and steam propulsion make warships impervious to incendiary damage, it is time to replace your Fire Vessels and Rocket Boats with a new weapon — the Torpedo Boat. This is a fast attack boat whose tasks are to fire slow-moving torpedoes into enemy warships, and are highly effective if used to attack surface craft in large numbers. As light attack craft, they are faster than Ironclads, but are at a disadvantage against the faster Steam Frigates which can dodge their weapons and then close in to retaliate.
For most non-Western factions that do manage to survive long enough, the Torpedo Boat is the most common unit that they will be raising most of the time. They are for most of the time fairly cheap and quick to build, thus making them ideal to "equalise" the board against the heavier and more sophisticated Western navies since they can be used to knock out most wooden warships with one or two hits, and an ironclad with four or five,
If you happen to be facing a Torpedo Boat-happy faction such as Germany , the Arabs or China, the answer here is very clear — build up your coastal defences and keep a firm eye on your Harbours. Because Torpedo Boats lack any means to engage buildings, fortifying your coastal towns is never a bad idea. Place down Citadels or Bastions to shadow the coast, and your enemy's Torpedo Boats won't be able to come near without being destroyed.
Torpedo boats (and a similar stealthed concept, attack submarines) first emerged in the American Civl War, but it was not until the Pacific War between Peru and Chile that they began to become more prominent. The first torpedo boats, built by the Confederate Navy to lift the blockade by American warships, were designed to function somewhat like Classical Mediterranean vessels in that they would ram their target with a spear loaded with a time bomb, and then move away.
However, this design wasn't always successful, and it was not until the emergence of the self-propelled torpedo, perfected by the Austrians with English help that such ships would be noticed by other navies.Torpedo boats came to prominence first during the Pacific War where their size and speed helped them to function not just as anti-ship weapons, but as scout units as well. During the Russo-Japanese War, both belligerents deployed extensive numbers of torpedo boats, as well as submarines.