The type UG was designed through the Dutch dummy company NV Ingenieurskantoor voor Scheepsbouw Den Haag (I.v.S) to circumvent the limitations of the Treaty of Versailles, and was built by foreign shipyards.

[9] Most Type VIIA U-boats were constructed at Deschimag AG Weser in Bremen with the exception of U-33 through U-36, which were built at Friedrich Krupp Germaniawerft, Kiel.

They were more heavily armed than the smaller Type II U-boats they replaced, with four bow and one external stern torpedo tubes.

Usually carrying 11 torpedoes on board, they were very agile on the surface and mounted the 8.8-centimetre (3.5 in) quick-firing deck gun with about 220 rounds.

[9] The boat was powered on the surface by two MAN AG, 6-cylinder, 4-stroke M6V 40/46 diesel engines, giving a total of 2,100 to 2,310 brake horsepower (1,570 to 1,720 kW) at 470 to 485 rpm.

When submerged it was propelled by two Brown, Boveri & Cie (BBC) GG UB 720/8 double-acting electric motors, giving a total of 750 horsepower (560 kW) at 322 rpm.

The Type VIIC was an effective fighting machine and was seen almost everywhere U-boats operated, although its range of only 8,500 nautical miles was not as great as that of the larger Type IX (11,000 nautical miles), severely limiting the time it could spend in the far reaches of the western and southern Atlantic without refueling from a tender or U-boat tanker.

[11] Type VIIC differed from the VIIB only in the addition of an active sonar and a few minor mechanical improvements, making them 2 feet longer and 8 tons heavier.

[11] On the surface the boats (except for U-88, U-90 and U-132 to U-136 which used MAN M6V40/46s) were propelled by two supercharged Germaniawerft, 6 cylinder, 4-stroke M6V 40/46 diesels totaling 2,800 to 3,200 PS (2,100 to 2,400 kW; 2,800 to 3,200 shp) at 470 to 490 rpm.

A battery of 86 mm line-carrying anti-aircraft rockets was tested (similar to a device used by the British in the defense of airfields), but this idea proved unworkable.

Only five torpedoes were carried, preloaded in the tubes, to free up space needed for additional gun crew.

Four VIIC boats were modified for use as surface escorts for U-boats departing and returning to French Atlantic bases.

Conversion began on three others (U-211, U-263, and U-271) but none was completed and they were eventually returned to duty as standard VIIC attack boats.

The modified boats became operational in June 1943 and at first appeared to be successful against a surprised Royal Air Force.

If the U-boat dived, surface vessels were called to the scene to scour the area with sonar and drop depth charges.

They would have had a much stronger pressure hull, with skin thickness up to 28 mm (1.1 in), and would have had a nearly 40% deeper crush depth as the previous VIICs.

When submerged the boat used two AEG GU 460/8-276 electric motors giving a total of 750 shp (560 kW) at 285 rpm.