Sjölejonet-class submarine

The Sjölejonet class was a series of nine coastal patrol submarines operated by the Swedish Navy during World War II and early Cold War. The boats were developed as part of a Navy modernization program intended to counteract Germany during the late 1930s. The boats were the first indigenous Swedish design, and incorporated unique weapons. During World War II, the boats conducted patrols along the coast to maintain Swedish neutrality. By the start of the Cold War, the vessels were retrofitted before being withdrawn from service by the early 1960s and being replaced by the Sjöormen class.

Throughout the 1930s, Sweden became increasingly concerned regarding German expansionism and greater Nazi influence in the Baltic. As a result, the Riksdag began an initiative to modernize and reformed the military.^[1]: 368 That decade, the Navy was in the process of replacing World War I-era submarine fleet with new boats. As part of this effort, the Sjölejonet class was intended to be small submarines ideal for patrols along the Swedish coast. The design featured a length of 210 feet 8 inches (64.21 m), beam of 21 feet (6.4 m), and a draught of 11 feet 2 inches (3.40 m). They featured a complement of 35 and were propelled by two MAN Diesel engines which produced 2,100 brake horsepower (1,600 kW) and two electric motors that produced 1,000 shaft horsepower (750 kW) through two propellers. While surfaced, the submarines had a maximum speed of 16 knots (30 km/h; 18 mph) and a displacement of 580 tons; when submerged, they had a speed of 9 knots (17 km/h; 10 mph) and displacement of 760 tons.^{[2]: 176-177}

While previous Swedish submarines were based on foreign designs, the Sjölejonet class were the first indigenous designed Swedish submarines. The most unique aspect of the submarines was their armament. They were equipped with six 533 mm (21.0 in) torpedo tubes: three mounted in the bow, one in the stern, and two in remotely-controlled rotating mounts on the deck in a system similar to French submarines. On the deck were also two 40 mm (1.6 in) deck guns on top of disappearing mounts, which was common on Dutch submarines.^{[2]: 176-177 [3]: 69}

Three submarines were initially ordered from Kockums, in Malmö, which were completed by 1939. As tensions increased by the end of the decade, another six were ordered,^{[2]: 177 [3]: 69} and were completed by 1942.^[1]: 374 The submarines were deployed to maintain Swedish neutrality during World War II. On 4 September 1942, Sjöborren collided with a ship and sank, although she was later repaired and brought back into service. In the 1950s, the submarines were refitted: the sail was streamlined, and both the deck guns and deck torpedo tubes were removed. The submarines were stricken between 1959 and 1964,^[2]: 177 with several names reused on new Sjöormen-class submarines in 1964.^[4]: 235