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.