They were minelaying submarines and were based on the British L-class submarine, HMS L55, which was sunk during the British intervention in the Russian Civil War.

The boats were of the saddle tank type and mines were carried in two stern galleries as pioneered on the pre-war Russian submarine Krab (1912).

Groups 3 and 4 had more powerful engines and a higher top speed.

Considered a new project, the hull was based on the Srednyaya class.

This group added stern torpedo tubes and new, more powerful diesel engines.