The Naval Military and Air Situation , the report made to the War Cabinet for the week ending 21st September 1939
The loss of HMS Courageous is the most significant incident noted with respect to Britain in the past week. There is the also first mention that “there is the suspicion that magnetic mines are being used”.
31. Any hopes that the Poles may have had of reforming their forces in the south-east were shattered by the Soviet invasion which began early on 17 September. Only some 100,000 frontier guards were available to meet this threat and there was no serious resistance.
By the morning of 20 September the Soviet high command claimed that their forces had penetrated to an average depth of 120 miles from the frontier and occupied VILNA, OLITA and BERESTOVITSA (30 miles east of BIALYSTOK). Cavalry and tank units had reached the suburbs of LWOW.
Reasons for Polish collapse.
32. Apart from the numerical superiority of the Germans and the subsequent Russian invasion, the main causes of the Polish collapse appeared to have been as follows: –
(a) Overwhelming German air superiority.
The initial attacks on aerodromes, flying schools and aircraft factories crippled the Polish air force. Subsequent air attacks on the railways and on columns of troops reduced the mobility of the Polish ground forces most seriously and prevented the development of an effective counter offensive. Later, air attacks on the headquarters of the Polish armies and government paralysed the direction of the country’s military and civil activities. These attacks were particularly effective, as the Germans frequently succeeded in locating headquarters either through the espionage system or by directional wireless.
(b) Mechanised forces.
The Poles were surprised not only by the weight of attack but also by the depth to which German mechanised forces operated independently of their main forces. In the initial stages the operations of German armoured formations were important factor in preventing the Poles stabilising the battle. Latterly, however, the Poles seem to have achieved considerable successes against isolated German armoured and motorised troops.
The Poles overestimated their own and underestimated the German strength. They appear to have assumed that the lack of roads would paralyse German motorised forces and give the advantage in a war of movement to their own horse cavalry. Consequently they made few defensive preparations. As one observer put it “the Polish army of 1939 was admirably prepared for the war of 1918”.
(d) The late withdrawal of the Western Army.
The head of the British military mission considers that the retreat of the army from the Poznan salient started two days too late. The absence of these eight divisions seriously compromised the effort to halt on the BUG and VISTULA.
33. An analysis of the dates of the various preparatory measures taken by the Red Army supports the view that the major decisions were taken after it became clear that an early collapse of the Polish armies was at least highly probable.
Reports indicate that the Soviet government awaited the completion of the very considerable mobilisation which they were carrying out in the West before assuming action. The advance the Red Army started early on 17 September and was naturally rapid as there was little resistance.
There are signs that, in spite of the professions of mutual good faith, the Soviet action was not entirely welcome to the Germans, and may even have been made to forestall them; but, on the other hand, there is some evidence to show that the Soviets were prepared to risk war with Great Britain.
Such was the British analysis even before the Poles had surrendered.