G7a torpedo

It was a steam-powered design, using a wet heater engine burning decaline, with a range of 7,500 metres (24,600 ft) at 40 knots (74 km/h; 46 mph) speed.

The TI was the last naval torpedo of German design in operational use with the traditional standard wet heat method of propulsion.

The torpedo's speed was determined by the level of pressure (three settings for 30/40/44 kn) from the low-pressure regulator feeding air to the bottom of the combustion chamber.

Though this system of propulsion gave the TI great speed and endurance it had the distinct disadvantage of being very noisy and leaving a long wake of bubbles, common to most non-electric torpedoes of the period, with the exception of the Japanese surface-launched Type 93 and submarine-launched Type 95, which were propelled by engines using pure oxygen as the oxidizer.

For U-boats, this relegated the TI 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.

Both mechanisms were flawed and contributed to the German "Torpedokrise" (Torpedo Crisis) which lasted from the start of the war and through 1942.

Also, the depth mechanism had a design-issue leading to leakage of vacuum when stored on the U-boats, causing the torpedo to run deep.

On 14 September 1939, U-30 was attacked by loitering United Kingdom Fairey Swordfish naval bombers when she fired a TI from her stern torpedo tube at the SS Fanad Head.