Pravda-class submarine
The "Pravda" class or P-class submarines were built for the Soviet Navy in the mid-1930s. They originally served as training ships, then later served in World War II for mainly transport duties. They were intended to operate with the surface fleet but failed to meet specifications, particularly for surface speed. The initial design envisaged guns for surface action. These boats had a long building time, being laid down in 1931 and completed in 1936. They were double hull boats with eight compartments. Their main shortcomings were underpowered machinery, a long diving time and poor seakeeping. Weakness  in hull strength had to be remedied by stiffening and weight cutting. Yakubov and Worth state that these were the least successful Soviet submarines of this era and were relegated to secondary duties on completion. The two surviving boats had their conning towers re-built to resemble the later K class. Ships. Three boats were built by Ordzhinikidze Yard Leningrad. All served with the Baltic Fleet. A fourth boat was planned but not laid down