Torpedoes are cigar-shaped underwater missiles with explosive warheads and are propelled either by internal engines or battery-powered electric motors. They are fired from submarines, ships, or aircraft to target surface vessels and submarines. Torpedoes are named after electric rays or torpedo rays that dwell on the seabed and emit electricity as a hunting and defensive mechanism. American inventor Robert Fulton coined the term during the 19th-century Napoleonic Wars when he called his experimental naval mine a torpedo.
The Swedish Torpedo 617, or TP 617 torpedo, is used on the Challenger-class and Archer-class submarines of the Republic of Singapore Navy (RSN) and is designed to strike enemy surface ships. Weighing 1,870 kilograms and measuring seven metres long, it is no surprise that the TP 617 is called a heavyweight torpedo. Like most modern torpedoes, it is wire-guided. This means that a thin wire reeling from the torpedo connects it to the submarine’s fire control system. This allows the submarine to transmit commands to the torpedo, controlling its speed and course while it relays its position and depth back to the submarine. The torpedo is also guided by sound signals, such as sonar, to help it identify targets.
The TP 617 is an export variant of the TP 613 torpedo, which was designed and manufactured by Swedish defence company Förenade Fabriksverken (now Saab Dynamics AB). The TP 613’s design was based on a British Mark 12 or Fancy torpedo that relied on high-test peroxide, a form of highly concentrated hydrogen peroxide, as a propellant. However, the fuel was known to be unstable. Two British Mark 12 torpedoes exploded on the submarine HMS Sidon on 16 June 1955 before a test-firing session, and the torpedo programme was terminated in 1959. Despite this, the British shared details of their design studies and failure evaluations of the Mark 12 torpedoes with the Swedish Navy. The Navy managed to fix the problems and incorporated the technology into the development of their successful TP 61 torpedo series, which includes the TP 617 torpedoes. Still in use today, the TP 617 is a significant part of the RSN’s past and present submarine capabilities.