Torpedoes are shot from submarines, not "fired". "Fire" is a Hollywood term when referring to a torpedo launch; in real life, the word "fire" means only one thing on a submarine, so that there is a clear distinction between the two terms.

Torpedoes are shot from submarines using one of two methods: water impulse ejection, or swim out. Both methods have been used for decades, since the beginning of modern submarine designs.

Swim outs are rarely, if ever, used in modern submarines, unless there's an emergency or the impulse system is down. If it's necessary, the torpedo tube is flooded, and the outer tube doors are opened, the torpedo engine is activated, and the weapon "swims out" of the tube toward the target.

Before 1969, torpedo electrical checks were performed with the weapon on the rack in the torpedo room. Since the loss of the USS Scorpion, widely believed to have been sunk by a hot-running torpedo during electrical checks that detonated before deactivation, all torpedoes are now electrically checked while the weapon is in the torpedo tube. This is a precaution in case the weapon engines activate during checks; if it does, it can swim out or be ejected.

Water impulse ejection is the most common method. Each horizontal torpedo tube, when flooded, is connected via another vertical tube to a third tube which has a piston ram in it. One side of the piston has water, which is the same as the water which floods the tube. The other side is connected to a high pressure air flask, capable of dumping about 3000psi instantly into the air side of the piston ram.

During target tracking, when a target shooting solution is calculated (both by hand, plot, and computer) the information is fed electronically into the torpedo's guidance system. The Commanding Officer will order "Firing Point Procedures" in the Control Room, which is the final step before launching the weapon. At the proper angle, and when the weapon is ready, the CO will order "Shoot", and the crew will send a command to the air flask, which immediately dumps air into the piston ram. The air pressure, which is higher than the outer sea pressure, forces the water out of the tube, along with the the torpedo itself. Once the torpedo has traveled a certain distance from the boat, the engine will start, and it will begin its journey toward the target. As a safety precaution, the torpedo needs to be a certain range away from the boat before the warhead arms to prevent it locking onto the boat it was launched from. If you're sleeping next to the tube in one of the crew spaces, or in the torpedo room itself (portable racks), the noise will wake you up if you're not used to it.

Though most torpedo solutions are derived over time by tracking a target, there are procedures to deal with an immediate threat as well. If Sonar detects a hostile torpedo in the water being launched, the hostile torpedo bearing can quickly be input into the torpedo guidance system, and "Snap Shot" toward the hostile torpedo's bearing. All modern torpedoes are both wire-guided and have active-passive homing sonar. If they lock onto a target, they are nearly impossible to evade, despite what Hollywood would have people believe.

Ejecting water in an empty tube during tube testing is called shooting "water slugs". It's not powerful enough to affect a boat underway, but its' strong enough to move a mooring bumper in port while moored next to a pier.

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