They carried two 5.9-inch guns, two 22 pounders, two torpedo tubes, and 12 torpedoes.

They could keep the sea for quite four months without being dependent on a supply ship or base.
The later _submarine cruisers_ were double-hulled, 275-320 feet long, had a surface speed of 16-18 knots, and a submerged speed of about 7 to 8 knots.

They carried either one or two 5.9-inch guns, six torpedo tubes, and about 10 torpedoes.

They had a very large radius of action, viz., from 12,000 to 20,000 miles, at a speed of 6 knots.

A large number (some 30 to 40) of these boats were under construction at the time of the Armistice, but very few had been completed.
There were two or three types of _U-boats_.