# Cruiser submarine

A cruiser submarine was a very large submarine designed to remain at sea for extended periods in areas distant from base facilities. Their role was analogous to surface cruisers; 'cruising' distant waters, commerce raiding, and otherwise operating independently. When operating within a fleet, cruisers and cruiser submarines could be expected to scout for and screen the battle fleet. Cruiser submarines were successful for a brief period of World War I, but were less successful than smaller submarines during World War II. Large submarines remained vulnerable to damage from defensively equipped merchant ships (DEMS), were slow to dive if found by aircraft, offered a large sonar echo surface, and were less able to defensively maneuver during depth charge attacks.

## History

The cruiser submarine concept originated during the unrestricted submarine warfare campaign of 1917. Three German Type U 139 submarines and seven former merchant submarines, each armed with two 15-centimetre (5.9 in) guns, patrolled areas distant from their North Sea bases to sink Allied merchant shipping as part of an effort to end World War I by starving the United Kingdom of Great Britain and Ireland. These distant patrols enjoyed unique immunity to the defensive convoy measures which limited successful submarine attacks in the vicinity of the British Isles.
The First World War combat experience of these submarines encouraged all major navies to build submarine cruiser prototypes between the world wars, but their cost discouraged most from further production. Developments were further limited by the London Naval Treaty of 1930, under which each signatory was permitted to possess no more than three large submarines, each above 2,000 tons (2,032 metric tons) but not exceeding 2,800 tons (2,845 metric tons) standard displacement, with guns not exceeding 6.1 in (150 mm) in caliber.
Japanese focus on the distances of their Pacific trade routes encouraged development of the widest variety of submarine cruisers, notably the types Junsen (巡潜, "Cruiser Submarine") including the types J, A, B, and C. Germany decided against building projected 3,140-ton type XI U-boats with an aircraft hangar and four 5-inch (13 cm) guns. Long-range submarines with less impressive deck guns, including Type IXD2 U-boats and United States Navy fleet submarines, evolved through the Second World War; and may be identified as cruiser submarines in comparison to submarines designed for shorter patrols over lesser distances.

## Examples

| Name | Nation | Surface displacement | Submerged displacement | Speed | Guns | Torpedo tubes | Crew | Year |
| Ettore Fieramosca | Kingdom of Italy | 1,530 tons | 2,094 tons | 15 knots (28 km/h; 17 mph) | 1 × 12cm (4.7 in) 45 caliber | 14 | 78 | 1929 |
| Surcouf | France | 3,250 tons | 4,304 tons | 18 knots (33 km/h; 21 mph) | 2 × 203mm (8in) 50 caliber | 10 | 118 | 1934 |
| Narwhal-class | USA | 2,730 tons | 4,050 tons | 17 knots (31 km/h; 20 mph) | 2 × 6"/53 caliber | 6 | 90 | 1928 |
| Type U-139 | Germany | 1,930 tons | 2,483 tons | 15 knots (28 km/h; 17 mph) | 2 × 15 cm (5.9 in) | 6 | 62 | 1916 |
| Type U-151 | Germany | 1,512 tons | 1,875 tons | 12 knots (22 km/h; 14 mph) | 2 × 15 cm (5.9 in) | 6 | 56 | 1917 |
| Type J1 | Japan | 2,135 tons | 2,791 tons | 18 knots (33 km/h; 21 mph) | 2 × 14 cm (5.5 in)/40 caliber | 6 | 80 | 1926 |
| Type B1 | Japan | 2,584 tons | 3,654 tons | 23 knots (43 km/h; 26 mph) | 1 × 14 cm (5.5 in)/40 caliber | 6 | 100 | 1940 |
| Type A3 | Japan | 3,603 tons | 4,762 tons | 16 knots (30 km/h; 18 mph) | 1 × 14 cm (5.5 in)/40 caliber | 6 | 100 | 1944 |
| HMS X1 | Royal Navy | 2,780 tons | 3,600 tons | 19 knots (35 km/h; 22 mph) | 4 × 5.2 in (13 cm) | 6 | 110 | 1923 |
| Type Kaidai | Japan | 1,833 tons | 2,602 tons | 23 knots (43 km/h; 26 mph) | 1 × 12 cm (4.7 in) | 6 | 80 | 1930 |
| K-class | Soviet Union | 1,490 tons | 2,104 tons | 22.5 knots (41.7 km/h; 25.9 mph) | 2 × 10 cm (3.9 in) | 10 | 67 | 1939 |
| Type IXD2 | Germany | 1,616 tons | 1,804 tons | 19 knots (35 km/h; 22 mph) | 1 × 10.5 cm (4.1 in) | 6 | 57 | 1938 |
| Cagni class | Italy | 1,461 tons | 2,136 tons | 18 knots (33 km/h; 21 mph) | 2 × 10 cm (3.9 in) | 14 | 85 | 1940 |