Type U 66 submarine

Class overview
Builders	Germaniawerft, Kiel[1]
Operators	Imperial German Navy
Preceded by	German Type U 63 submarine
Succeeded by	German Type UE I submarine
Built	1913–15
In commission	1915–18
Completed	5
Lost	3
Scrapped	2
Preserved	0
General characteristics (as U-7 class)[2]
Type	submarine
Displacement	695 long tons (706 t) surfaced 885 long tons (899 t) submerged
Length	228 ft (69.50 m) (o/a)
Beam	20 ft 8 in (6.30 m)
Draft	12 ft 5 in (3.79 m)
Propulsion	1 × shaft 2 × Germania 6-cylinder four-stroke diesel engines, 2,269 shp (1,692 kW) total 2 × SSW electric motors, 1,223 shp (912 kW) total
Speed	17 knots (31 km/h; 20 mph) surfaced 11 knots (20 km/h; 13 mph) submerged
Range	1,200 nautical miles (2,200 km; 1,400 mi) at 12 knots (22 km/h; 14 mph) 100 nmi (190 km; 120 mi) at 4 knots (7.4 km/h; 4.6 mph)
Complement	unknown
Armament	5 × 45 cm (17.7 in) torpedo tubes (four bow, one stern) 9 torpedoes 1 × 6.6 cm (2.6 in) L/26 deck gun
General characteristics (as Type U 66)[3]
Type	submarine
Displacement	791 t (779 long tons) surfaced 933 t (918 long tons) submerged
Length	69.50 m (228 ft) (o/a) 54.66 m (179 ft 4 in) (pressure hull)
Beam	6.30 m (20 ft 8 in) (o/a) 4.15 m (13 ft 7 in) (pressure hull)
Height	7.95 m (26 ft 1 in)
Draft	3.79 m (12 ft 5 in)
Installed power	2 × Germania 6-cylinder four-stroke diesel engines, 2,300 PS (1,692 kW; 2,269 shp) total 2 × electric motors, 1,260 PS (927 kW; 1,243 shp) total
Propulsion	1 × shaft, 1 × 1.80 m (5 ft 11 in) propeller
Speed	16.8 knots (31.1 km/h; 19.3 mph) surfaced 10.3 knots (19.1 km/h; 11.9 mph) submerged
Range	7,370 nmi (13,650 km; 8,480 mi) at 8 knots (15 km/h; 9.2 mph) surfaced 115 nmi (213 km; 132 mi) at 4 knots (7.4 km/h; 4.6 mph) submerged
Test depth	50 m (160 ft)
Complement	4 officers, 32 enlisted men
Armament	5 × 45 cm (17.7 in) torpedo tubes (four bow, one stern) 12 torpedoes 1 × 8.8 cm (3.5 in) SK L/30 deck gun, later replaced by 10.5 cm (4.1 in) SK L/45 deck gun

The Type U 66 was a class of five submarines or U-boats operated by the German Imperial Navy (German: Kaiserliche Marine) during World War I. The class is alternately referred to as the U-66-class or the Type UD. The class was built by Germaniawerft of Kiel to their 506d design as the U-7-class for the Austro-Hungarian Navy. The five boats were sold to the Imperial Germany Navy at the beginning of World War I when it was thought impossible for the submarines to reach the Mediterranean for delivery to Austria-Hungary.

The Austro-Hungarian Navy, after competitively evaluating six submarines of three foreign designs, selected the Germaniwerft 506d or Type UD design over a design from Whitehead & Co. for the U-7 class. The boats, numbered U-7 to U-11, were designed to be 69.50 m (228 ft 0 in) long and displace between 695 and 885 tonnes (684 and 871 long tons) when surfaced and submerged. They were to be armed with five torpedo tubes and a deck gun. For propulsion the design called for twin diesel engines for surface running and twin electric motors for subsurface movement. The Austro-Hungarian Navy ordered the boats in February 1913 and construction began on the first boats in November.

After the outbreak of World War I in August 1914, the Austro-Hungarian Navy became convinced that delivery of the still-unfinished submarines to the Mediterranean via Gibraltar would be impossible. As a result, they sold the five boats to the Imperial German Navy in November 1914. The German Navy assigned the numbers U-66 to U-70 to the five submarines and had them redesigned and reconstructed to their specifications. These changes, which included a larger deck gun, increased the displacement of the U-boats by almost 100 tonnes (98 long tons) surfaced and nearly 50 tonnes (49 long tons) submerged.

All five boats saw active service, and four sank 15 or more ships. Only U-68, sunk six days into her first war patrol in March 1916, had no successes. Two other boats, U-66 and U-69 disappeared in 1917. The remaining two U-boats, U-67 and U-70, were surrendered to the United Kingdom and were broken up by 1921.