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  The order was given in April 1946 to design a "duplex" artillery system to replace the obsolete 122 mm gun M1931/37 (A-19), 152 mm howitzer-gun M1937 (ML-20) and other World War II era field guns, such as 122 mm Model 1931, 152 mm Model 1910/30, 152 mm Model 1935 (BR-2).