The two submarines of the Orzel class were designed and constructed in the Netherlands. Originally four boats were planned but only two were approved. They were ordered as a result of worsening relations between Poland and Germany. The first one - Orzel, was paid for by public subscription and the second - Sep, was paid for out of normal Naval Directorate funds.
These large ocean going submarines, ordered in 1935, proved to have excellent fighting qualities. They were of 'double hull' type, with a pressure hull of 5 compartments. Diving limit was 100 m, and radious 7000 nm at 10 kts / 100 nm at 5 kts. Orzel commissioned on 2.II.1939 and Sep arrived at Gdynia in April 1939 before builder's trials had been concluded, to avoid the danger of German sabotage. Orzel sunk during the war, but Sep returned to Poland on 25.X.1945 and served in Polish Navy until 1969.