OVERVIEW: The Tp 421 is a lightweight, submarine-launched, wire-guided torpedo developed by Sweden in 1979. It provides dual-role capability for anti-submarine and anti-surface warfare on Nacken-class submarines.

DETAILS: “Tp” stands for Torped. The Tp 421 is part of the Swedish Tp 4 series, derived from Tp 42 variants optimized for submarine use on the Project A14 Nacken class. It measures approximately 2.6 m in length with a 400 mm diameter, uses electric propulsion powered by a silver‑zinc battery, and carries a ~45 kg high-explosive warhead. Guidance is via wire during the mid-course phase with active/passive acoustic homing for terminal engagement against both underwater and surface threats, with an approximate effective range of 7.4 km. The Tp 421 entered service in 1979, replacing earlier Tp 412 torpedoes on Swedish submarines.

TYPE: Lightweight Wire-Guided Dual-Purpose Torpedo

FUNCTION: Launched from 400 mm submarine torpedo tubes, the Tp 421 travels under wire guidance initially, switches to active/passive acoustic homing in its terminal phase, and is used against both submerged submarines and surface ships.

NOTE:
IOC: 1979 (Tp 421)
Manufacturer: Sweden (Förenade Fabriksverken / FFV)
Operators: Sweden
Platforms: Project A14 Nacken-class submarines

SOURCE:
Jane’s Naval Weapon Systems (“Torpedoes, Sweden” – Tp 41–46 overview) ; cmano-db.com A‑14 Nacken weapon fit (Tp 421) – https://cmano-db.com/submarine/174/ and https://cmano-db.com/cw/submarine/407/ ; Military Periscope Europeana Tp 421 artifact – https://www.europeana.eu/en/item/916108/smm_mm_object_MM25302