To determine this, one must first take a good look at what weapon really kills ships on a regular basis (not including the rare lucky hit). While the dive bomber attack at the June, 1942 Battle of Midway, and the sinking of the Arizona by aircraft at Pearl Harbor in December, 1941, are spectacular instances of bombs sinking ships, bombs are not the most reliable ship-killers. Bombs punch holes in a ship, start fires and can do damage, but a ship can still float, because the bombs merely let air in, and thus, the ship still floats. The most reliable way to sink a ship is to fill it full of water that is should be displacing.
To do that, you need to punch holes in the hull of a ship under the waterline. Bombs dropped from airplanes could not do this. However, in the 1860s, modern torpedoes were invented, and eventually became capable of hitting the side of a ship with a rather large amount of explosive (up to 600 pounds), punching a hole in the ships hull, letting in lots of water. Submarines have often been the prime delivery method of torpedoes, and have used them to great effect.
Some of the famous torpedo victims have been the liner Lusitania in World War I, the USS Oklahoma (hit by multiple aircraft-launched torpedoes at Pearl Harbor in 1941), the USS Wasp (hit by three submarine torpedoes in September, 1942), the Argentine cruiser General Belgrano (hit by two Mk 8 torpedoes in 1982), and the HIJMS Yamato (ten torpedo hits from torpedo bombers during the battle of 1945 Okinawa) and Musashi (19 torpedoes during Leyte Gulf Musashi also took 17 bomb hits).
Today, aircraft no longer carry torpedoes to attack surface ships experience in World War II showed that it could often lead to heavy losses among the attacking planes for little result. Instead, aircraft began to carry missiles for the role. This would hit the headlines in 1982 when Argentine Super Etendards carried Exocets in successful attacks on the British vessels HMS Sheffield and Atlantic Conveyor. Anti-ship missiles, particularly sea-skimming missiles, add some of the benefits of a torpedo (hits near the waterline) and also can cause much of the damage that bombs cause. This includes starting fires. In 1982, HMS Sheffield and Atlantic Conveyor did not sink right away, they sank as a result of the fires caused by the unused fuel from the missiles. Often, these missiles are launched far enough away so that the aircraft face little chance of losses. The missiles can be shot down, but the launching platform will survive and be back for another try later.
Submarines, though, have also received new weapons. An American nuclear attack submarine would carry the Mk 48 ADCAP torpedo, which has a range of 34 kilometers, and delivers a 650-pound warhead of PBXN-103 (equivalent to over 1200 pounds of TNT). The ADCAP not only has working guidance systems (both wire-guidance and an active-passive sonar system), but the magnetic fuses work reliably. This which means that the explosive charge detonates underneath a ships keel usually breaking ships as large as a Spruance-class destroyer in half. Subs also can carry the Harpoon anti-ship missile, which has a range of 140 kilometers, and delivers a 500-pound warhead.
So, which of these is deadlier? The submarine is persistent in a sense it is a mobile minefield that can sit around, and control an area of ocean for a period of time. But its sensors are limited and often the victims must come to it (it rarely sends messages the transmissions can be detected and submarines are better when they are the hunters, not the hunted). Aircraft can get to a target faster, can detect targets further away, but they lack persistence (once they fire their weapons, they must return to base, reload, refuel, and the pilot must get rest). Much of this depends on what the target is. A Ticonderoga-class cruiser has more to fear from submarine-fired torpedoes than aircraft or missiles from any source, primarily due to the Aegis air defense system. On the other hand, Japanese destroyers will probably have more to fear from aircraft and missiles, due to the fact that they have superb anti-submarine warfare suites, but a limited (16 Sea Sparrow surface-to-air missiles) air-defense suite. Often, the platforms and the quality of the crews aboard those platforms involved will determine what is the most lethal threat to a surface vessel. Harold C. Hutchison (firstname.lastname@example.org)
The history of naval warfare since 1914 is all about a steady increase in threats to surface ships. The emergence of the submarine and airplane have produced the most new threats, but which of these threats is the deadliest?