The SH-4 developed between 1925 and 1928 into a compact boat carrying two 18-inch torpedoes and a machine gun. Its conning position and hull form gave it useful stability in heavy weather, helping justify the distinctive Soviet approach. Orders accumulated gradually until roughly fifty-five boats were in service by 1937. The class was divided among the Baltic, Black Sea, and Pacific fleets rather than concentrated in one theatre. By the end of the decade, poor maintenance had caused many surviving boats to be reclassified as submarine chasers. A workable design had lost its intended combat role through neglected upkeep.
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SH-4 production, seakeeping, and maintenance decline
The compact SH-4 proved stable in heavy weather and spread across three fleets, but poor upkeep pushed many boats into submarine-chaser classification by the late 1930s.