During the 1930s, in the lead-up to World War 2 (1939-1945), the Soviet Union invested in an all-new class of submarine known as the Pravda-class (or P-class). These numbered four planned vessels of which one was cancelled (P4) and three saw completion from the period of 1931 until 1936. These went on to serve from 1935 until 1956. The boats had a conventional diesel-electric propulsion scheme and, early on, were used to train new generations of Soviet submariners but, as war enveloped the Soviet Union, the types were pressed into service as at-sea transports mainly due to their inherently limited design as attack platforms.
As built, the boats had a surfaced displacement of 1,200 tons and a submerged displacement of 1,870 tons. Overall length measured 295.3 feet. Power was from a diesel-electric arrangement which produced 5,400 horsepower for surface running and 1,400 for undersea running. These drove a twin-shaft arrangement at the stern. Reachable speeds amounted to 20.5 knots surfaced and 11.8 knots submerged. Range was out to 5,700 nautical miles. The double-hull design was tested to depths of 340 feet. Aboard was a crew of fifty-four.
Armament included four torpedo tubes at the bow and two at the tern with ten torpedo reloads between them. The bow- and stern-facing mountings allowed the boat to engage surface targets both forward and aft without needing to turn the entire vessel around to face the enemy. For surface attack, the vessels were outfitted with 2 x 100mm deck guns and a 45mm Anti-Aircraft (AA) measure. The original specification called for 2 x 130mm deck guns but this was not to be.
The boat's profile ran long with a raised, blunt bow and uneven deck line. The sail was of an elongated design which gave it a low profile on the horizon. The forward and aft sections of the hull were tapered in their natural directions with the aft section containing the twin propeller arrangement straddling the rudder control.
Because of their protracted construction periods, the boats languished behind contemporaries when they were introduced and were soon found to lack the power and hull strength required for any heavy-duty military work. They were additionally slow to dive and fared poorly in open-water, particularly in rough sea states where the boat could be violently tossed about. As such, the types were not a success by the time they entered service in the immediate pre-war period and were soon assigned to second-line roles because of their deficiencies.
The four boats of the P-class were Pravda (P1, the lead ship of the class), Zvezda (P2) and Iskra (P3). P1 and P3 were both launched in 1934 with P2 following in 1935. P1 was the only one of the class to be sunk, this off the coast of Finland in September of 1941. P3 managed a career into 1952 and P2 outdid them all by lasting until 1956. Both P2 and P3 had their sails completely reworked at a later time to better reflect the improvements of the succeeding K-class submarines - the largest boats produced by the Soviets during the World War 2 period. Twelve of this group were constructed.