If a critical point is struck, one torpedo may be enough. A good rule of thumb is to look at the tonnage. One torpedo per 2500 tons. This is a real rough guesstimate and only applies to SHIII. As far as torpedo types, the TI G7e steam torpedo is a decent, all-around torpedo. The only drawback is the wake lets everyone and their brother know where the torpedo is. The TII G7e electric torpedoes are only good at ambushing lone or poorly supported escorts at close range. Their short range (3km) really hurts this torpedo's practicality. FaT and LuT Torpedoes vary in its ability to change course. One is a pattern runner (FaT), which is good for packed convoy. The LuT can carry a second gyroangle so unnecessary maneuvering for firing is not needed.
What you really want are G7 acoustic homers. Destroyers do not like these things.
