The Boat
Torpedoes and Mines
A. Torpedoes
The meat and drink of the attack submarine was the torpedo. Unlike the original Type VIIA U-boat that carried eleven torpedoes, the Type VIIB was armed with a complement of fourteen so-called "tin fish", five of which were already placed ready to fire, four in the bow tubes and one in the single stern tube. The other nine were stowed on board, a situation that made the living conditions, particularly at the beginning of a patrol, cramped and at times unbearable. Two torpedo types were carried during the part of the war in which U-47 operated - the pre-war type G7a or T1, which was propelled by compressed air, and the more advanced battery-powered G7e or T2 "electric" torpedo, which unlike its predecessor was a silent, wakeless device.
Side view of a Type G7 Torpedo
Both torpedo types were used due to the fact that they offered different advantages; the fact that the G7e was wakeless allowed U-boat skippers to attack during daylight, as the device didn't leave a tell-tale trail of bubbles, while the G7a was employed at night, as they were faster and had a greater range. Both devices were fitted with magnetic pistols, though impact pistols were fitted in an attempt to correct problems experienced during the Norwegian campaign of 1940, the beginning of what was called the Torpedo Crisis.
G7a Compressed air torpedo
Date in service: c.1938
Length: 7.19m (23.5ft)
Diameter: 53.3cm (21in)
Weight: 1528kg (3369lbs)
Propulsion: Decahydronapthalene (Decalin) wet heater
Warhead: 280kg/616lbs Hexanite
Pistols: Magnetic/Impact
Range: 6000m at 44 knots/8000m at 40 knots/14000m at 30 knots
G7e Wakeless torpedo
Date in service: c.1939
Length: 7.19m (23.5ft)
Diameter: 53.3cm (21in)
Weight: 1603kg (3534lbs)
Propulsion: Two 26-cell acid batteries
Warhead: 200kg/640lbs Hexanite
Pistols: Magnetic/Impact
Range: 5000m at 30 knots
B. Mines
The Type VIIB was also equipped with twenty-six mines, which allowed the submarine to perform its secondary strategic function as a minelayer. Although minelaying was an important role, it was not popular among U-boat crews - in addition to neither having the effectiveness nor the "immediacy" of a torpedo strike, the sense of achievement for the captain and crew was also far lower. The mines employed consisted of three main types - the "floating" type TMA (Torpedo mine A), the magnetic TMB (Torpedo mine B), and later the powerful TMC (Torpedo mine C). All of these mines were laid by releasing them from the torpedo tubes.
Torpedo Mine A (TMA)
Date in service: c. 1935
Charge: 350kg (772lbs)
Type: Surface impact mine
Torpedo Mine B (TMB)
Date in service: c. 1939
Charge: 420-560kg (926-1235lbs)
Type: Ground-influence magnetic mine
Torpedo Mine C (TMC)
Date in service: c. 1940
Charge: 860-930g (1896-2050lbs)
Type: Ground-influence magnetic mine
