Simply put, a torpedo is a self propelled underwater missile that carries an explosive warhead to a target. Early torpedoes damaged their target by exploding as soon as it made contact. These torpedoes were called contact torpedoes. Newer torpedoes can detonate once in close proximity to a target. These proximity torpedoes do not even have to touch the ship to inflict damage upon it. A contact torpedo is one that has to physically hit the target to detonate. It accomplishes this through a contact fuse housed in the torpedo’s nose.
The method in which a contact torpedo causes damage is actually a two step process.
The initial explosion of the torpedo’s warhead causes a large gas bubble to form. Because this bubble expands so quickly, it forms a shockwave. Once this bubble/shock wave strikes the ship’s hull, it punches the hull plates in, rupturing the hull. The energy radiating out from the point of contact is enough to tear surrounding plates off of the hull. This forms a large hole in the ship’s hull.
Following the creation of the bubble, the displaced water around it rapidly begins pushing back. Once the bubble finally collapses, the water rushes back in to fill the void. Because contact torpedoes cause the bubble to form against the ship’s hull, the returning water collects right at the rupture formed by the initial explosion. With so much water rushing into this point, it forces a very strong jet of water to enter the rupture. This water jet can be powerful enough to punch through bulkheads or plating already weakened by the initial blast.
In addition to the blast wave itself, shrapnel is created from the pieces of the ship torn away in the explosion. Traveling at extremely high speeds, these projectiles can perforate the insides of the ship, causing extensive damage and further compromising watertight integrity.