# Type U 31 submarine

Type U 31 was a class of U-boats built during World War I by the Kaiserliche Marine.
Between 1912 and 1915 eleven were built on Germaniawerft in Kiel, amongst these top-three-scoring U-35 with the famous Lothar von Arnauld de la Perière as commander, U-39 with Walter Forstmann and U-38 with Max Valentiner. Together these U-boats sunk more than 1,198,139 gross register tons (GRT).
Later admiral and head of the Abwehr from 1935 to 1944 Wilhelm Canaris also served as commander on two different Type U 31 U-boats. He first took over from Max Valentiner on U-38 and later on U-34.

## Design

German Type U 31 submarines were double-hulled ocean-going submarines similar to Type 23 and Type 27 subs in dimensions and differed only slightly in propulsion and speed. They were considered very good high sea boats with average manoeuvrability and good surface steering.
Type U-31s had an overall length of 64.70 m (212 ft 3 in), their pressure hulls were 52.36 m (171 ft 9 in) long. The boats' beam was 6.32 m (20 ft 9 in) (o/a), while the pressure hull measured 4.05 m (13 ft 3 in). Type 31s had a draught of 3.56 m (11 ft 8 in) with a total height of 7.68–8.04 m (25 ft 2 in – 26 ft 5 in). The boats displaced a total of 971 tonnes (956 long tons); 685 t (674 long tons) when surfaced and 878 t (864 long tons) when submerged.
Type U-31s were fitted with two Germania 6-cylinder two-stroke diesel engines with a total of 1,850 metric horsepower (1,361 kW; 1,825 bhp) for use on the surface and two Siemens-Schuckert double-acting electric motors with a total of 1,200 PS (883 kW; 1,184 shp) for underwater use. These engines powered two shafts each with a 1.60 m (5.2 ft) propeller, which gave the boats a top surface speed of 16.4 knots (30.4 km/h; 18.9 mph), and 9.7 knots (18.0 km/h; 11.2 mph) when submerged. Cruising range was 8,790 nautical miles (16,280 km; 10,120 mi) at 8 knots (15 km/h; 9.2 mph) on the surface. Diving depth was 50 m (164 ft 1 in).
The U-boats were armed with four 50 cm (20 in) torpedo tubes, two fitted in the bow and two in the stern, and carried 6 torpedoes. Most boats received one or two 8.8 cm (3.5 in) SK L/30 deck guns, which were later replaced with 10.5 cm (4.1 in) SK L/45 guns on some. The boats' complement was 4 officers and 31 enlisted.

## List of Type U 31 submarines

There were eleven Type U 31 submarines commissioned into the Kaiserliche Marine.
| Boat | Armament | Fate |
| U-31 | no deck gun | lost in January 1915 in the North Sea – Discovered 2012 off the East Anglia Coast and identified September 2015 |
| U-32 | two 8.8 cm guns, from 1916/17 one 10.5 cm gun | sunk 5 May 1918 north-west of Malta |
| U-33 | one 8.8 cm gun, from 1916/17 one 10.5 cm gun | surrendered 1919, scrapped |
| U-34 | one 8.8 cm gun, from 1916/17 one 10.5 cm gun | sunk October 1918 in the Mediterranean Sea |
| U-35 | one 7.5 cm gun (1914), one 10.5 cm gun (1916) | surrendered 1918, scrapped |
| U-36 | two 8.8 cm guns, from 1916/17 one 10.5 cm gun | sunk 24 July 1915 west of Rona, Hebrides |
| U-37 | two 8.8 cm guns, from 1916/17 one 10.5 cm gun | sunk by mine in April 1915 in the English Channel |
| U-38 | one 8.8 cm gun, from 1916/17 one 10.5 cm gun | surrendered 1919, scrapped |
| U-39 | one 8.8 cm gun, from 1916/17 one 10.5 cm gun | sunk 18 May 1918 off El Ferrol |
| U-40 | one 8.8 cm gun | sunk 23 June 1915 in the North Sea |
| U-41 | one 8.8 cm gun | sunk 24 September 1915 in the English Channel |