G7a torpedo
The G7a or G7a/T1 was the standard issue Kriegsmarine
The Kriegsmarine was the name of the German Navy during the Nazi regime . It superseded the Kaiserliche Marine of World War I and the post-war Reichsmarine. The Kriegsmarine was one of three official branches of the Wehrmacht, the unified armed forces of Nazi Germany.The Kriegsmarine grew rapidly...

The modern torpedo is a self-propelled missile weapon with an explosive warhead, launched above or below the water surface, propelled underwater towards a target, and designed to detonate either on contact with it or in proximity to it.The term torpedo was originally employed for...

 during the early years of World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...



The torpedo was 53.3cm (21in) in diameter, 7.163 m (23 ft 6 in) in length, and with a warhead of 280 kg (617 pd) of Hexanite
Hexanite was a castable German military explosive developed early in the 20th century before the First World War for the Kaiserliche Marine, intended to augment supplies of trinitrotoluene , which were then in short supply. Hexanite is significantly more powerful than TNT on its own...

, and was standard issue for all U-boat
U-boat is the anglicized version of the German word U-Boot , itself an abbreviation of Unterseeboot , and refers to military submarines operated by Germany, particularly in World War I and World War II...

s of the war.

The torpedo was of a straight-running unguided design, stabilized by a gyroscope
A gyroscope is a device for measuring or maintaining orientation, based on the principles of angular momentum. In essence, a mechanical gyroscope is a spinning wheel or disk whose axle is free to take any orientation...

. The G7a was of variable speed, running a distance of 6,000 m at 81 km/h (6,600 yd at 44kt), 8,000 m at 74 km/h (8,800 yd at 40 kt), and 14,000 m at 55.6km/h (15,300 yd at 30 kt). The 44 kt 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
Cylinder (engine)
A cylinder is the central working part of a reciprocating engine or pump, the space in which a piston travels. Multiple cylinders are commonly arranged side by side in a bank, or engine block, which is typically cast from aluminum or cast iron before receiving precision machine work...

 reciprocating engine
Reciprocating engine
A reciprocating engine, also often known as a piston engine, is a heat engine that uses one or more reciprocating pistons to convert pressure into a rotating motion. This article describes the common features of all types...

, 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 World War II - it had the distinct disadvantage of being very noisy and leaving a long wake of bubbles, common to most torpedoes of the period, with the exception of the Japanese Type 93
Type 93 torpedo
The Type 93 was a -diameter torpedo of the Imperial Japanese Navy , launched from surface ships. It is commonly referred to as the Long Lance by most modern English-language naval historians, a nickname given it after the war by Samuel E. Morison, the chief historian of the U.S...

 and submarine Type 95
Type 95 torpedo
The Type 95 torpedo was a torpedo of the Imperial Japanese Navy.It was based on the formidable Type 93 torpedo but had a smaller warhead, shorter range and a smaller diameter...

, which were fuelled by enriched oxygen. 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.

The G7 was fitted with a magnetic exploder, which was inadequately tested (like the U.S. Navy's Mark XIV
Mark 14 torpedo
The Mark 14 torpedo was the United States Navy's standard submarine-launched anti-ship torpedo of World War II.This weapon was plagued with many problems which crippled its performance early in the war, and was supplemented by the Mark 18 electric torpedo in the last 2 years of the war...

), having never been live fired. In addition, because the G7's performance had been never been assessed, between deep running and premature explosions (both also familiar to the Mark 14), the G7 suffered a thirty percent failure rate early in World War II. The response of the high command, ignoring complaints and blaming the operators, was also common to the U.S. Pacific Fleet's Submarine Force. The problems were so serious, Admiral Dönitz
Karl Dönitz
Karl Dönitz was a German naval commander during World War II. He started his career in the German Navy during World War I. In 1918, while he was in command of , the submarine was sunk by British forces and Dönitz was taken prisoner...

 said, "...never before in military history has a force been sent into battle with such a useless weapon."


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
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

 Fairey Swordfish
Fairey Swordfish
The Fairey Swordfish was a torpedo bomber built by the Fairey Aviation Company and used by the Fleet Air Arm of the Royal Navy during the Second World War...

 naval bomber
A bomber is a military aircraft designed to attack ground and sea targets, by dropping bombs on them, or – in recent years – by launching cruise missiles at them.-Classifications of bombers:...

s when she fired a G7a from her stern
The stern is the rear or aft-most part of a ship or boat, technically defined as the area built up over the sternpost, extending upwards from the counter rail to the taffrail. The stern lies opposite of the bow, the foremost part of a ship. Originally, the term only referred to the aft port section...

 torpedo tube
Torpedo tube
A torpedo tube is a device for launching torpedoes. There are two main types of torpedo tube: underwater tubes fitted to submarines and some surface ships, and deck-mounted units installed aboard surface vessels...

 at the SS Fanad Head
SS Fanad Head
The SS Fanad Head was a British cargo steamer. She was torpedoed and sunk in the Second World War.-Early history:The Fanad Head was built by Workman, Clark & Co Ltd, Belfast for G. Heyn & Sons Ltd. She was completed in 1917 and homeported in Belfast...

. U-30 was undamaged in the attack and served until she was scuttled
Scuttling is the act of deliberately sinking a ship by allowing water to flow into the hull.This can be achieved in several ways—valves or hatches can be opened to the sea, or holes may be ripped into the hull with brute force or with explosives...

 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
G7e torpedo
The G7e or more appropriately the G7e/T2, G7e/T3, and G7e/T4 Falke torpedoes were, with the exception of the T4 model, the standard torpedoes for Germany during World War II...

/T3 electric torpedo in 1942, largely due to the inferior performance and tendency of the G7e/T2 (the wakeless electric torpedo available to U-boats from 1939-1942) to fail to detonate, both on proximity and contact fuse
Contact fuse
A contact fuze, percussion fuze or direct-action fuze is the fuze that is placed in the nose of a bomb or shell so that it will detonate on contact with a hard surface....


The G7a could be fitted with both the FaT (ladder search pattern) and LUT pattern running guidance system
Guidance system
A guidance system is a device or group of devices used to navigate a ship, aircraft, missile, rocket, satellite, or other craft. Typically, this refers to a system that navigates without direct or continuous human control...

s for attacking convoy
A convoy is a group of vehicles, typically motor vehicles or ships, traveling together for mutual support and protection. Often, a convoy is organized with armed defensive support, though it may also be used in a non-military sense, for example when driving through remote areas.-Age of Sail:Naval...



  • Bekker, Cajus. Hitler's Naval War. New York: Zebra Books/Kensington Publishing Corp., 1977. (Reprints 1974 MacDonald and Jane's 1971 translation of Gerhard Stalling Verlag edition)
  • Blair, Clay, Jr. Silent Victory. New York: Bantam, 1976. (Reprints Lippincott 1975 edition)

External links

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