What damage can torpedoes do?

Answer 1

Historically, torpedoes were impact weapons - they detonated when coming into contact with a ship's hull. As most torpedoes carried a fairly large explosive warhead (at least 100lbs of TNT equivalent, up to 500lbs in some cases), this punched a very large hole in the hull of the ship, and the shock wave produced could damage large sections of the interior.

Impact torpedoes generally killed their target in one of two ways: flooding or fire. The large hole the initial explosion would cause would let in a large amount of water, and the shock wave would almost certainly damage a significant amount of the ship's internal watertight bulkheads. It was easily possible that such flooding could not be contained quickly enough, and the ship would loose buoyancy, founder, and sink. Alternately, the initial explosion commonly caused flammable materials inside the ship to catch fire, and fire on a ship (even a metal-hulled one) is extremely dangerous, as there are large amounts of flammable materials all over the ship itself. Most critically, any ammunition or fuel which caught fire could lead to a catastrophic explosion, destroying the entire ship in a massive fireball.

The more recent development is the proximity torpedo. This was first exemplified during WW2 by the magnetic-fused torpedo, which would detonate not on impact with the hull, but when it sensed that it was "close enough" to a large metal object. Modern torpedoes have similar sensors, which enable them to detonate directly underneath the target vessel. This is extremely deadly, as a powerful explosion directly underneath (no more than 10-20 beneath the ship's bottom) a ship will cause a large bubble of air, as the explosion pushes out the water from that area. This air bubble results in a large section of the ship's keel being completely unsupported; the weight of the ship is thus unsupported, causing the keel to buckle and possibly break. This method of attack can effectively rip a ship in two using the ship's own weight against it. Even if the ship survives this stress, the buckling and secondary effects of the explosive shock wave can cause serious internal damage, possibly resulting in a fire or other internal problem, enough to cripple the ship.

Today, a single solid torpedo hit against most civilian cargo ships is fatal in the large majority of cases. Likewise, single torpedo hits are generally fatal to naval vessels up to about frigate size. Destroyers and cruisers are more likely to survive a torpedo hit, but unlikely to survive two or more, and even a single hit can cause crippling damage. Aircraft carriers and similar very large combat ships can probably survive several hits, but are still very much threatened by a single torpedo hit in critical areas. Most modern submarines find a single torpedo hit fatal, but some of the larger ones may survive it, and the exact location of the torpedo hit on a submarine is very much a determining factor in its survival.