'Dirschau' was a German operation, the first genuinely military undertaking of World War II, designed to ensure the survival of the railway bridge over the lower reaches of the Vistula river at Tczew (Dirschau in German) in northern Poland, which the Germans needed for their advance across northern Poland to link East Prussia and Pomerania in 'Weiss' (i) (1 September 1939).

The strategic background to the undertaking was the need of Generaloberst Fedor von Bock’s Heeresgruppe 'Nord' to push General Günther von Kluge’s 4^th Army eastward across the 'Danzig corridor' as rapidly as possible from the main body of Germany to link with General Georg von Küchler’s 3^rd Army in East Prussia.

The bridge was of strategic importance, and as the threat of war loomed increasingly closer, the Polish government in August 1939 ordered that all the bridges across the Vistula river be fitted with gates, rail locks and demolition charges. This was noted by the Germans, who planned a special forces raid to secure the bridge at Tczew. A scheduled German freight train was to cross the bridge immediately before the start of hostilities, and this would require the Poles to open the locks and gates. At this point German warplanes were to attack and destroy the local command post and the firing wires connecting it with the bridges using information which, before this, the pilots of the Junkers Ju 87 single-engined dive-bombers had fixed in their minds while travelling as passengers on the railway service. Immediately after the destruction from the air of the Poles' ability to demolish the bridge, pioneer parties of the 41^st Pionierbataillon hidden on the train were to disembark, strip the detonators from the demolition charges, and drive the Polish defenders away from the target area. Finally, a following armed freight train was to destroy any surviving Polish defenders and disgorge men to hold the bridge until relieved by advancing German grounds forces.

The Polish railway administration had been informed that on 1 September a German freight train of 65 wagons would pass over the railway bridge. At 03.08, the train crossed from East Prussia into Poland, and steamed into Marienburg (now Malbork) for the locomotive to be changed. The change was performed by German railway personnel in Polish uniforms after the Polish workers had been killed: these latter thus became the first casualties of the yet-undeclared World War II. Behind this first train which, as noted above, was operating a scheduled service, there followed a second but unscheduled armoured train, whose personnel killed most of Polish railway staff they encountered. However, in one village a Polish officer became suspicious and began to examine the first train’s cargo and transit papers, which caused a 15-minute slip in the train’s schedule and caused the second train began to close on the first. The German special forces personnel who had occupied the Polish checkpoints in the Danzig corridor became so worried that they shot 20 of the Polish railway and customs personnel they had seized, but even so one of the Poles was able to telephone and warn the defences of Tczew before he was killed.

The Polish defenders immediately closed and locked the gates, and prepared to blow the bridge before the Germans could arrive at 04.45.

At 04.26 three Ju 87B-1 dive-bombers took off from Elbing, and seven minutes later destroyed their targets at the bridge: the first of the Stukas' bombs landed 12 minutes before the official start of the war, which was signalled by the shelling of Westerplatte at 04.45 by the 280- and 150-mm (11.02- and 5.91-in) guns of the training ship (pre-Dreadnought battleship) Schleswig-Holstein.

Even though the Poles could not blow the bridge, the two German trains could not start to cross, and the fixed defences denied the special forces the ability to undertake their tasks. With the freight train halted well to the east of the bridge, the armoured train could not use its firepower effectively even from a position close behind the freight train. At a point 110 yards (100 m) to the east of the bridge, the German troops clambered out of the freight train but could not successfully approach even as the Polish defenders worked feverishly to complete new firing circuits for the demolition charges. At 06.10 the Poles managed to blow the eastern bridge pier, and 30 minutes later the western pier, and the outer spans of the bridge collapsed into the Vistula river.

German troops took the destroyed bridges one a day later, and by 15 October German engineer had completed a single-track temporary rail bridge. A year after the explosion, the new double-track bridge went into operation, and this was almost wholly destroyed by the Germans during the evening of 8 March 1945 as they pulled back from the Soviet advance toward Germany.