'Frisches Haff' was the German plan for the defence of the fortified area of Danzig and Gotenhafen (Gdynia) against the Soviet 'Danzig Offensive Operation' within the 'East Pomeranian Strategic Offensive Operation' (7/31 March 1945).
This area was the main port for refugees fleeing to the west from the Soviet advance into and through East Prussia, and General Dietrich von Saucken, commander of the 2nd Army within Reichsführer-SS Heinrich Himmler’s (from 21 March Generaloberst Gotthard Heinrici’s Heeresgruppe 'Weichsel' ordered the defence of the area for as long as possible in order to keep the evacuation routes open.
Marshal Sovetskogo Soyuza Konstantin K. Rokossovsky’s 2nd Belorussian Front began its offensive on 15 March 1945, the primary drive, toward the coast at Zoppot between Gdynia and Danzig, being undertaken by General Polkovnik Vasili F. Popov’s 70th Army and General Polkovnik Ivan T. Grishin’s 49th Army advancing in parallel. The fighting was savage, but by 19 March the Soviet spearheads had reached the heights above Zoppot, while Generalleutnant Clemens Betzel’s 4th Panzerdivision had been pushed back to the outskirts of Danzig. By 22 March the 70th Army had reached the south coast of the Baltic Sea, thereby splitting the German defence. The Soviets took Gdynia on 26 March, its defenders and many civilians retreating to the headland at Oksywie, from where they were evacuated to the Hel peninsula.
Danzig finally fell on 28 March 1945, after which the remnants of the 2nd Army withdrew to the delta of the Vistula river to the north-east of the city. Evacuation of civilians and military personnel from there and from the Hel peninsula continued until 10 May 1945.
According to Soviet claims, in the Battle of Danzig the Germans lost 39,000 men killed and 10,000 taken prisoner.