Battle of Gdynia Battle of Gdynia was one of the major battles in northern Poland during the Invasion of Poland of 1939 . The Germans ' main push towards Gdynia began on 8 September and they captured Gdynia less than a week later on 14 September . Before the battle . Gdynia is a major civilian and military port on the Baltic Sea , and was an important industrial centre of the Second Polish Republic . Its defence was one of the key elements in the Polish defence plan . One of the Polish armies , Armia Pomorze , had orders to prevent German forces from breaking through the Polish Corridor that linked most of Germany with East Prussia and to defend Gdynia , Hel , Kępa Oksywska and Oksywie . The forces defending Gdynia were grouped under the Land Coastal Defence ( " Lądowa Obrona Wybrzeża " ) , commanded by Colonel Stanisław Dąbek and Naval Coastal Defence ( " Morska Obrona Wybrzeża " ) Captain Stanisław Frankowski . The Polish plan foresaw that the Germans would manage to cut off Gdynia from the main forces of Armia Pomorze ; therefore , the Land Coastal Defence was tasked with defence of the coast for 8 – 10 days and promised reinforcements after that period . It was thus prepared for individual operations and reassigned from Armia Pomorze to the Polish Navy , and Stanisław Dąbek received orders directly from counter - admiral Józef Unrug . The Polish Navy would support the coastal defence with 1 destroyer ( ORP " Wicher " ; 3 other destroyers had been evacuated from the Baltic Sea during Plan Peking ) , 1 heavy minelayer ( ORP Gryf ) and several submarines and smaller surface ships . On 1 September , the Polish Land Coastal Defence force had a strength of approximately 17 , 000 ( increased from about 5 , 000 two months earlier ) , with 40 artillery pieces ( including 8 anti - aircraft ) , 34 mortars and granade launchers and approximately 400 machine guns . Infantry units were placed : The German forces tasked with the capture of Gdynia were commanded by General Leonhard Kaupisch and formed part of the Army Group North under General Fedor von Bock . They were approximately 29 , 000 strong , with over 300 artillery pieces , 70 mortars and grenade launchers and 700 machine guns . The German Navy ( Kriegsmarine ) in the area consisted of 2 old battleships , 3 cruisers , 10 destroyers and several smaller units . Approximately 120 Luftwaffe planes were supporting the German forces . The battle . The German offensive isolated the Polish coast from the Polish mainland between 4 and 8 September , and Armia Pomorze was forced to retreat south - east . Units of Land Coastal Defence has been engaged by the German forces from 1 September , although it was not until the second week of the war that the Germans would begin a direct assault on the Polish port of Gdynia . The German Navy , operating in the area with the pre - dreadnought " Schleswig - Holstein " and smaller units shelled Polish positions , but with limited effect and prevented from closing on the coast by Polish coastal batteries . The German land offensive was much more successful . German forces established a connection between Germany and Prussia by 4 September . After heavy fighting near Kartuzy ( 5 September ) , their main attack towards Gdynia began on 8 September , and after intense fighting near Puck and Wejherowo ( 8 September ) step by step the Poles were forced back towards the sea . When the Polish positions outside Gdynia were overrun , and in view of the retreat of the Armia Pomorze , on 10 September Colonel Dąbek decided to abandon Gdynia in order to avoid civilian casualties during the city fighting , and thus on 12 September he ordered all Polish units to retreat from Gdynia toward Kępa Oksywska , a fragment of the coast near Puck Bay . On 11 and 12 September the fights near Mechlinki transformed into an incessant two - day battle , after which Polish troops had to retreat again . The Germans captured Gdynia on 14 September . Kępa Oksywska was not prepared for siege or provisioned for the approximately 9 , 000 strong remaining Polish forces and in the battle of Kępa Oksywska the Poles sustained heavy losses ( approximately 2 , 000 ) . After a last failed counterattack on 19 September , Colonel Dąbek , who participated in the front line battle and was wounded , decided to issue order to surrender and committed suicide after giving the order to cease fire . The Polish Navy was tasked to provide support to Gdynia through Plan Worek ( submarine operations ) and Operation Rurka ( mining sea approaches ) . These plans did not prevent defeat .