The German submarines may be divided into four classes, viz.:  Submarine cruisers, U-boats, U.B.-boats, U.C.-boats.  There were several variations of each class.

The earlier submarine cruisers of the “Deutschland” class were double-hulled vessels, with a surface displacement of 1,850 tons, and were about 215 feet long; they had a surface speed of about 12 knots and a submerged speed of about 6 knots.  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.  The earlier vessels were 210 to 220 feet long, double-hulled, with a surface displacement of about 750 tons, a surface speed of 15 to 16 knots, and a submerged speed of about 8 knots.  They carried one or two 4.1-inch guns, four to six torpedo tubes, and about 10 torpedoes.

Later vessels of the class were 230 to 240 feet long, and of 800 to 820 tons surface displacement, and carried six torpedo tubes and 16 torpedoes.  Some of them, fitted as minelayers, carried 36 mines, and two torpedo tubes, but only two torpedoes.  A later and much larger class of minelayers carried a 5.9-inch gun, four torpedo tubes, 42 mines, and a larger number of torpedoes.  The earlier U-boats could keep the sea for about five weeks without returning to a base or a supply ship; the later U-boats had much greater sea endurance.

The smaller U.B.-boats were single-hulled, and about 100 feet long, had a surface speed of 7 to 9 knots and a submerged speed of about 5 knots, and carried one 22-pounder gun, two torpedo tubes and four torpedoes.  These boats could keep the sea for about two weeks without returning to a base or supply ship.  A later class were double-hulled, 180 feet long, with greater endurance (8,000 miles at 6 knots), a surface speed of 13 knots and a submerged speed of 8 knots; they carried one 4.1-inch gun, five tubes and 10 torpedoes.

The earliest U.C.-boats were 111 feet long, with a surface displacement of 175 tons, a surface speed of 6-1/2 knots, and a submerged speed of 5 knots.  They carried 12 mines, but no torpedo tubes, and as they had a fuel endurance of only 800 miles at 5-1/2 knots, they could operate only in southern waters.

The later U.C.-boats were 170 to 180 feet long, double-hulled, had a surface speed of 11 to 12 knots and a submerged speed of about 7 knots, carried 18 mines, three torpedo tubes, five torpedoes, and one 22-pounder gun, and their fuel endurance was 8,000 to 10,000 miles at a speed of 7 to 8 knots.