A Torpedo is a name used for any long-range missile carried by a space ship or used in a space battle. Despite the fact that they are missiles, for some reason, GW along with certain Sci-Fi works like Star Wars, likes to call them as Torpedoes for...some reason, despite lacking the functionality of a torpedo.
Torpedoes are basically used by every faction in 40k that has a Navy, yes, that includes the Tyranids as well. These are pretty large weapons, with anti-ship being up to 200 feet in length and are powered by a plasma reactor, which makes up part of the warhead as well as the method of propulsion. Standard torpedoes move in a straight line and have limited sensing and targeting abilities, turning to intercept if they come within a few thousand kilometres of their target, although often they will still miss. You would expect that every faction should have some sort of heat-seeking or homing capabilities am I right?
Torpedoes are highly effective weapons in space combat. They are apparently small and fast enough that only defence turrets and fighters can catch and destroy them easily before they impact, although using weapons batteries, lances and Nova Cannons can prove effective if the captain is desperate enough. Torpedoes come in all shapes and sizes, with different torpedoes armed with unique warheads intended for a particular situation.
- Boarding Torpedo - For its more tacticool cousins.