The Mk 46 is a lightweight torpedo of US origin. It was developed in the early 1960's to replace the successful Mk 44 torpedo. It was the first high performance thermal powered torpedo in US service. The complex but powerful propulsion system was chosen to keep up with Soviet submarine developments. The Mk 46 is the most common lightweight torpedo in the world and remains in widespread use.

The Mk 46 has a conventional layout with the homing section and warhead in the nose, the fuel in the middle and the engine and control fins at the rear. Apart from the original production version all Mk 46 use an Otto fuel engine. Over time the design was improved with improved guidance, stronger body, new fuel and two speed engine.

The Mk 46 uses a passive and active sonar guidance system. Over time the quality of the seeker has been improved. The seeker on the Mk 46 Mod 2 reportedly has a detection range of 460 meters. The latest models received various upgrades to improve performance in shallow water.

The Mk 46 has a range of 8 km and a speed of 40 to 45 kt. The NEARTIP improvement includes a two speed motor which extends the range up to 11 km. The Mk 46 can engage targets ranging from 15 to over 400 meters below sea level. The 45 kg warhead is more powerful than those used on many other lightweight torpedoes.

The Mk 46 is found on many surface vessels ranging from frigates to cruisers. The Mk 46 can also be air launched and is used on various helicopters such as the SH-60 Seahawk, the Sea King and the Lynx. The Mk 46 is also deployed by more unconventional means such as the Mk 60 CAPTOR mine and ASROC anti-submarine rocket.

The main user of the Mk 46 is the US navy. Subsequent upgrades ensure that the Mk 46 remains a capable weapon, although the very latest lightweight torpedo designs feature both better guidance and propulsion. The Mk 46 is in use with many NATO partners and various other US allies, making it the most numerous lightweight torpedo in the world.