The Invasion of Poland

Poland in 1939 had frontiers with Germany on three sides. East Prussia sat above it, Silesia below, and the Polish Corridor ran between the two halves of Germany to the sea. After the occupation of Czechoslovakia in March 1939 there was a fourth line of approach from the south. The border ran to about 1,750 miles and there was no natural obstacle on any of it.

The interior is flat, open and good tank country, cut by rivers running roughly north to south: the Warta, the Vistula, the Bug, the San. Any of those lines was defensible and all of them were behind the industrial regions and the population the army was expected to protect.

That is the whole strategic problem. The French and British urged a defence on the Vistula, which was militarily sound and meant conceding a third of the country and most of its industry before firing a shot. The Polish plan defended forward instead, on the assumption that a French offensive in the west within about fifteen days would relieve the pressure. There was no French offensive.

The German plan was a double envelopment: Army Group North from Pomerania and East Prussia, Army Group South from Silesia and Slovakia, closing behind the Polish armies west of the Vistula. Around 1.5 million men, sixty divisions and 2,750 tanks against roughly a million Poles, thirty-nine divisions and about 600 tanks, most of them light.

The Polish plan, Plan West, was built on a promise. The Franco-Polish alliance committed France to a general offensive by the fifteenth day of mobilisation. France mobilised, advanced a few miles into the Saar, stopped, and withdrew. Whether Poland could have held longer on the Vistula is arguable; that it was fighting on a schedule nobody else kept is not.

The decision that ended the campaign was taken in Moscow. The secret protocol to the Molotov-Ribbentrop Pact of 23 August had already divided the country. When the Red Army crossed on 17 September the Polish plan, which by then rested on holding a bridgehead in the south-east until French help arrived, became impossible in an afternoon.

The Polish army was not the obsolete force of the legend. It had a competitive anti-tank rifle, a good light tank in small numbers, and a fighter that was outclassed but flown well enough to cost the Luftwaffe several hundred aircraft. What it did not have was quantity, radios in useful numbers, or any answer to being attacked from three directions by an army with twice its divisions.

The single most consequential object in this campaign was not a weapon. It was a wooden box handed over at a forest villa near Warsaw five weeks before the invasion, containing a working reconstruction of the German Enigma machine.

The military figures are comparatively well documented. The civilian figures are not, and they begin during the campaign rather than after it: around 150,000 Polish civilians were killed in those five weeks, many of them in the bombing of undefended towns and in reprisal shootings carried out behind the advancing army.

The killing did not stop when the fighting did. Operation Tannenberg and the Intelligenzaktion that followed were prepared before the invasion and targeted the Polish educated class by name from lists compiled in advance. In the Soviet zone, around 22,000 Polish officers, police and officials were shot in the spring of 1940 at Katyn and elsewhere, and the Soviet Union denied it for fifty years.

The Polish record is held by the Institute of National Remembrance and the Polish Institute and Sikorski Museum in London, which holds the archive the government took with it. The German operational records are at Freiburg. Soviet records on the invasion and on Katyn were partially opened in the early 1990s and access has since narrowed.

The Enigma story rests on the Polish Cipher Bureau papers, on Marian Rejewski's own postwar account, and on the British files at Kew released from 1974 onwards, which is why almost nothing published before that date mentions it.