The Polish navy was unprepared for the scale of the German air and naval attacks launched on it beginning on 1 September 1939. Unrug, a former U-boat captain in the German Imperial Navy, foresaw the impending invasion and sent his three newest destroyers to Britain in late August. Unrug knew that the lack of Polish antiaircraft defenses and concentration of much more powerful German naval units in the southern Baltic made defeat inevitable. Those ships that remained behind at Gdynia and Gdansk endured two days of constant German air and naval attacks that damaged or sank all of them save submarines Orzel and Wilk, which managed to escape. Unrug and his staff withdrew to the naval base on the Hel peninsula after the invasion and were the last of the Polish military to surrender, on 2 October 1939. During the campaign, the Polish navy lost 26 vessels. Personnel casualties amounted to 1,500–2,000 men killed and perhaps 3,500 wounded.
Several naval personnel escaped to Britain to serve with the remnants of their navy reorganized under Royal Navy command. The Poles received two new destroyers from the British through an Anglo-Polish Naval Accord of 18 November 1939. The destroyer Grom and submarine Orzel were sunk during the German invasion of Norway, and the destroyer Burza was heavily damaged during the Dunkerque evacuation.
The Polish government-in-exile's navy remained active in the Allied war effort, thanks to a steady flow of recruits from Polish refugees in Britain and the addition of new British destroyers and gunboats. The Polish navy participated in a wide range of actions, including the sinking of the German battleship Bismarck, protection of trans-Atlantic convoys, and the amphibious assaults on Sicily and Normandy. The 4,000 Polish navy officers and sailors operating in conjunction with the British manned 47 warships (including 2 cruisers, 10 destroyers, and 5 submarines). They sank 9 enemy warships and 39 transport vessels. The Polish navy lost 3 destroyers and 2 submarines, and it suffered 404 dead and 191 wounded.
Divine, A. D. Navies in Exile. New York: E. P. Dutton, 1944.; Peszke, Michael A. Poland's Navy, 1918–1945. New York: Hippocrene Books, 1999.