SM UB-40^{[Note 1]} was a German Type UB II submarine or U-boat in the German Imperial Navy (German: Kaiserliche Marine) during World War I.

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SM UB-45 a U-boat similar to UB-40
History
German Empire
Name	UB-40
Ordered	22 July 1915[1]
Builder	Blohm & Voss, Hamburg[1]
Cost	1,152,000 German Papiermark[2]
Yard number	264[3]
Launched	25 April 1916[3]
Completed	18 August 1916[3]
Commissioned	17 August 1916[2]
Fate	Scuttled during the retreat from Belgium, 5 October 1918[2]
General characteristics
Class and type	German Type UB II submarine
Displacement	274 t (270 long tons) surfaced 303 t (298 long tons) submerged
Length	36.90 m (121 ft 1 in) o/a 27.90 m (91 ft 6 in) pressure hull
Beam	4.37 m (14 ft 4 in) o/a 3.85 m (12 ft 8 in) pressure hull
Draught	3.69 m (12 ft 1 in)
Propulsion	1 × propeller shaft 2 × 6-cylinder diesel engine, 284 PS (209 kW; 280 bhp) 2 × electric motor, 280 PS (210 kW; 280 shp)
Speed	9.15 knots (16.95 km/h; 10.53 mph) surfaced 5.81 knots (10.76 km/h; 6.69 mph) submerged
Range	6,450 nmi (11,950 km; 7,420 mi) at 5 knots (9.3 km/h; 5.8 mph) surfaced 45 nmi (83 km; 52 mi) at 4 knots (7.4 km/h; 4.6 mph) submerged
Test depth	50 m (160 ft)
Complement	2 officers, 21 men
Armament	2 × 50 cm (19.7 in) torpedo tubes 4 × torpedoes (later 6) 1 × 8.8 cm (3.5 in) Uk L/30 deck gun
Notes	42-second diving time
Service record[4]
Part of:	Flandern Flotilla 10 March 1916 – 2 October 1918
Commanders:	Oblt.z.S. Karl Neumann 17 August – 2 December 1916 Oblt.z.S. Hans Howaldt 3 December 1916 – 14 December 1917 Oblt.z.S. Karl Dobberstein 15 December 1917 – 17 May 1918 Oblt.z.S. Hans Joachim Emsmann 18 May – 31 July 1918
Operations:	28 patrols
Victories:	99 merchant ships sunk (129,330 GRT) 1 auxiliary warship sunk (6,287 GRT) 16 merchant ships damaged (60,629 GRT) 1 merchant ship taken as prize (470 GRT)

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A German Type UB II submarine, UB-40 had a displacement of 274 tonnes (270 long tons) when at the surface and 303 tonnes (298 long tons) while submerged. She had a total length of 36.90 m (121 ft 1 in), a beam of 4.37 m (14 ft 4 in), and a draught of 3.69 m (12 ft 1 in). The submarine was powered by two Körting six-cylinder diesel engines producing a total 284 metric horsepower (280 shp; 209 kW), two Siemens-Schuckert electric motors producing 280 metric horsepower (210 kW; 280 shp), and one propeller shaft. She was capable of operating at depths of up to 50 metres (160 ft).^[2]

The submarine had a maximum surface speed of 9.15 knots (16.95 km/h; 10.53 mph) and a maximum submerged speed of 5.81 knots (10.76 km/h; 6.69 mph). When submerged, she could operate for 45 nautical miles (83 km; 52 mi) at 4 knots (7.4 km/h; 4.6 mph); when surfaced, she could travel 6,450 nautical miles (11,950 km; 7,420 mi) at 5 knots (9.3 km/h; 5.8 mph). UB-40 was fitted with two 50 centimetres (20 in) torpedo tubes, four torpedoes, and one 8.8 cm (3.5 in) Uk L/30 deck gun. She had a complement of twenty-one crew members and two officers and a 42-second dive time.^[2]

The U-boat was ordered on 22 July 1915 and launched on 25 April 1916. She was commissioned into the German Imperial Navy on 17 August 1916 as SM UB-40.^{[Note 2]}

The submarine sank 100 ships in 28 patrols. UB-40 was scuttled in Ostend when the German army retreated from Belgium on 5 October 1918.^[2]

The wreck of UB-40 has been located & identified by divers in the recent years.^[5]