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HSwMS Sjoormen (A12)

Diesel-Electric Attack Submarine

HSwMS Sjoormen was the lead ship of her class and entered service with the Swedish Navy in 1968, serving until the early-1990s.
Authored By: Staff Writer | Edited: 11/12/2018
National Flag Graphic


Year: 1968
Status: Decommissioned, Out-of-Service
Ships-in-Class: 5
Named Ships: HSwMS Sjoormen; HSwMS Sjolejonet; HSwMS Sjobjornen; HSwMS Sjohunden; HSwMS Sjohasten
Roles: Hunter; Direct-Attack;
Complement: 25
Length: 167.3 ft (50.99 m)
Width: 29 ft (8.84 m)
Height: 19 ft (5.79 m)
Displacement (Surface): 1,185 tons
Displacement (Submerged): 1,500 tons
Propulsion: 2 x Pielstick diesel engines with 1 x ASEA electric motor driving power to x Shaft astern.
Speed (Surface): 15 kts (17 mph)
Speed (Submerged): 20 kts (23 mph)
Operators: Singapore (as RSS Centurion); Sweden
HSwMS Sjoormen ("Serpent") was a Cold War-era diesel-electric attack submarine designed, developed and built in Sweden for the Swedish Navy. much thought and care was given to making the Sjoormen-class a quiet, fast undersea hunter and this involved the fitting of rubber tiles to the single hull design. The class provided the Navy with decades of faithful service before the line of five boats was given up in favor of more modern designs. The class is also notable in becoming the first in naval history to utilize a cruciform rudder plane arrangement at the stern.

The Sjoormen-class succeeded the outgoing Draken-class of which six boats were built and operated from 1962 until 1988. The Sjoormen boats were, themselves, succeeded by the Nacken-class (A14) which numbered three units in all.

As built, the submarine displaced 1,185 tons when surfaced and 1,500 tons when submerged. Dimensions included an overall length of 165.7 feet, a beam of 20 feet and a draught of 19 feet. Propulsion was possible via the diesel-electric arrangement which involved a pair of Hedemora (Pielstick) diesel generators coupled with a single ASEA electric motor driving power to a single shaft astern. The boat could make surfaced speeds of 15 knots and submerged speeds of up to 20 knots. Aboard were twenty-five operating personnel made up of officers and enlisted and endurance was up to 21 days at sea. Armament was 4 x 21" (533mm) torpedo tubes and 2 x 16" (400mm) torpedo tubes - all bow-facing - and these could also be used for dispersing naval mines as needed. The hull was tested to depths of 490 feet.

HSwMS Sjoormen was ordered in 1961 and saw her keel laid down in 1966, eventually launching on January 25th, 1967. She was formally commissioned for service into the Swedish Navy in 1968 and served until the 1990s before being retired (decommissioned). A 1992 modernization effort did not include HSwMS Sjoormen in the plans and she was laid up as soon as 1993. It was in 1997 that the boat (along with her three sisters, the fifth boat was preserved) was sold to Singapore where it continued to operate under the RSS Centurion name. The Singapore Navy acquired the boat on May 28th, 1999 and commissioned it on June 26th, 2004. It maintains an active service status under the Singapore flag today (December 2017).


4 x 533mm (21") torpedo tubes (bow-facing).
2 x 400mm (16") torpedo tubes (bow-facing).

Optional: Mines carried in place of the torpedo supply.

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