G7a torpedo
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The G7a or G7a/T1 torpedo was the standard issue torpedo for Germany during the early years of World War II. The torpedo was of standard German specifications for all U-Boat torpedoes of the war at 53.3cm (21in) in diameter, 7.163m in length, and with a warhead of 280kg Hexanite.
The torpedo was of a straight running unguided design, stabilized by a gyroscope. The G7a was of variable speed, running a distance of 6km at 44kts, 8km at 40kts, and 14km at 30kts. The 44kts setting was used only by torpedo boats like the Schnellboote.
The G7a was the last torpedo of German design to use a wet heat method of propulsion. The torpedo was fueled by a mixture of compressed gas, decalin and water. The compressed gas was forced into a combustion chamber along with petrol and water, where the mixture was ignited; after which the resulting superheated steam powered a four cylinder reciprocating engine, in turn powering a pair of contra-rotating propellers.
Though this system of propulsion gave the G7a great speed and endurance - the greatest of any production model German torpedo of WWII - it had the distinct disadvantage of being very noisy and leaving a long wake of bubbles. This relegated the G7a for use mainly at night, when its wake was least noticeable, so as to not give away the element of surprise and the location of the submarine that fired it.
There is at least one recorded case of a U-Boat being bombed based upon her position being given away by a G7a's wake. On September 14, 1939, U-30 was attacked by loitering United Kingdom Fairey Swordfish naval bombers when she fired a G7a from her stern torpedo tube at the SS Fanad Head. U-30 was undamaged in the attack and served until she was scuttled at the end of the war.
Though the G7a was easily spotted by surface ships, it remained the torpedo of choice for some U-Boat captains until the release of the G7e/T3 electric torpedo in 1942, largely due to the inferior performance and tendency of the G7e/T2 (the wakeless electric torpedo available to German U-Boats from 1939-1942) to fail to detonate, both on proximity and contact fuses.
The G7a could be fitted with both the FaT (Also known as ladder search pattern) and LUT pattern running heads for attacking convoys.
