"In the late 1950's the Swedish Navy decided to develop lightweight torpedoes for the anti-submarine role in its submarines and later for surface and air launching. The first weapon to appear was the Forenade Fabriksverken (FFV) - produced Tp (Torped) 41 in the 1960's and from this was developed the homing torpedo Tp 411 then the Tp 412 for the 'Sjoormen' (A12) class submarines until replaced by the Tp 431 in 1988. In 1975 FFV produced the Tp 42 dual-purpose torpedoes of which the TP 421 was for the 'Nacken' class submarine, the Tp 422 was for anti-submarine helicopters while the Tp 423 was for the 'Goteborg' class frigates.

The latest lightweight weapon is the Tp 43, an evolutionary development of the Tp 42, which began development in the early 1980's and entered production for the Swedish Navy in 1987.

In May 1990 the Swedish FMV contracted Swedish Ordnance (formerly FFV) to complete development of a new version of Tp 43 with a new homing head as Tp 45. This will be either a new weapon to replace Tp 43 or it will be an upgrade of Tp 43.

On 1 July 1996 the Swedish Defence Material Command signed a project definition contract with Bofors Underwater Systems for the next generation lightweight torpedo, designated Tp 46 Grampus.

Bofors has also developed an integral fire-control system known as Spider for the Tp 43/Tp45.

Few details are available about the Tp 46 Grampus although it is known to be a 400 mm diameter, wire-guided weapon. The requirement is for a deep-diving, variable speed drive weapon with a maximum speed of 45 kt. It is intended that the weapon will be able to discover submarines on the bottom and report their discovery to the launch-platform."