The 21 cm Kanone 39 (K 39) was a Czech-designed heavy gun used by the Germans in the Second World War. Two were built before the Germans occupied Czechoslovakia in March 1939 and seized the rest of the guns and kept it in production for their own use, eventually building a total of 60 guns for themselves. They saw action in Operation Barbarossa, the siege of Odessa, siege of Leningrad and the siege of Sevastopol and were used on coast defence duties.