"Although the Mark 44 was successful, the Us Navy recognised that a better performance was required to meet the new threat from Soviet nuclear submarines and feasibility studies began in December 1956. These led to an operational requirement issued in November 1960 and to meet this, the Mark 44 was developed into the Mark 46 with production beginning in 1963 as Mark 46 Mod 0.

As the Soviet threat grew, a Near-Term Improvement Program (Neartip) began in October 1972. This was aimed at improving the acoustic performance, countermeasure resistance, guidance and control system and fire-control system. Prototypes were built from July 1974 and the operational evaluation of the torpedo was completed in November 1977.

An initial production award was made in July 1979 and this version became Mod 5. From 1981, this was the prime production version both as new-build and for upgrading of many Mod 2 weapons.

During the mid-1980s the Mod 5 was further upgraded as Mod 5A (S) and from 1989 both were introduced into service together with Mod 5A weapons.

With the growing threat from Soviet nuclear submarines it became clear that the Mark 46 could not provide an adequate response. In 1971, the US Navy began work on the Advanced Destroyer/Air Lightweight Torpedo (AD/ALT) programme with a technical assessment between February 1972 and September 1978. At the end of this phase, advanced development contracts became available and were awarded from May 1979 to McDonnell Douglas (EX-51) and Honeywell, later Alliant Tech Systems (EX-50), the later company briefly being part of the Hughes organization, which was absorbed by Raytheon in 1997.

The EX-50 proved the more promising design and was selected late in 1980 for further development with a full-scale engineering development contract awarded in September 1983. Full operational evaluation of the torpedo, designated Mark 50 Barracuda, was scheduled for completion in September 1990 but did not begin until July 1990 and was completed in May 1992, with the weapon entering service from October 1992 with final deliveries early in 1997.

The high cost of the Mark 50, estimated by one source at USD 250,000 compared with USD 180,00 for Mark 46, and the declining threat from nuclear submarines following the end of the Cold war, meant a re-evaluation of the US Navy's lightweight torpedo requirements. A Service Life Extension Programme (SLEP) of the Mark 46 was considered to ensure it remained viable until at least 2007 but a more practical solution proposed in 1994 was to merge the Mark 46 and Mark 50 as the Light Hybrid Torpedo (LHT) programme to enhance the Mark 46 with new technology to meet the threat from diesel electric submarines in shallow waters over the Continental Shelf.

A demonstrator (designated Control and Acoustic Test Vehicle) was produced during 1994 to show the practicality of merging the two weapons originally to be designated Mark 46 Mod 8 but redesignated Mark 54 in the summer of 1996. Technical and operational evaluation is anticipated in 2000 for completion by 2002 when full scale production is scheduled to begin."