On 17 September, as the XIX Corps secured Brest-Litovsk, the Soviet army invaded Poland. This action came as a complete surprise, not only to the Poles but to the German army, which had been kept in the dark over the secret clause in the Nazi-Soviet Pact of 23 August, which detailed the division of Poland between the two powers in the event of hostilities with Poland.
On 3 September, Foreign Minister von Ribbentrop had cabled Molotov, his Soviet opposite number, suggesting that Soviet forces should invade Poland’s eastern regions. The Germans were concerned that Poles might set up some form of administration in the eastern part of Poland which came under Soviet influence and, therefore, outside direct German control. The Soviets had had no knowledge of the date of the German invasion, and were themselves taken by surprise at the astonishing pace of the German attack. Nonetheless, Stalin wanted to ensure that the Soviet Union had control over eastern Poland, if only to build up a buffer zone between German-occupied Poland and the Soviet Union proper. Molotov was instructed to inform Ribbentrop that Soviet forces would cross the border when sufficient troops could be deployed – 17 September 1939.
The Soviet invasion force was divided into two ‘fronts’ (similar to army groups), totalling more than 20 infantry divisions, 15 cavalry divisions and nine tank brigades. The Byelorussian (White Russian) Front was led by Army Commander Kovalev (consisting of four small armies) and was tasked with the seizure of Polish territory from Brest-Litovsk northwards to the border with Lithuania. The Ukrainian Front of Army Commander Timoshenko (three small armies) was responsible for the invasion of Polish lands south of the Pripet Marshes, with Lwow being its main goal. The southernmost of the Ukrainian Front armies – Twelfth Army – was well equipped with mechanised forces, in order to cut off Polish forces attempting to retreat southwards to the safety of Romania and Hungary.
Polish forces in the east of Poland consisted merely of militia and frontier guards plus a few reserve cavalry squadrons. At first, some Polish troops thought that the Red Army might be coming to their assistance, especially when Soviet troops were seen to avoid combat with the Poles. But as the Red Army marched deeper into Poland – some Soviet mechanised spearheads penetrating as deep as 100km (60 miles) in the first two days – the situation became clearer: Polish units overrun by the Red Army were captured and quickly disarmed, and fighting broke out if the Poles resisted.
The already hopeless position facing the Polish high command was doubly confirmed by the Soviet invasion. The possibility of forming any sort of bridgehead around Lwow was undermined by the imminent arrival of Soviet forces on its right flank. Accordingly, the Polish high command instructed all troops to retreat back to Hungary and Romania to fight their way past German holding forces; but to try to slip past any Soviet forces unless physically obstructed by them. On 17 September, the Polish president and Government fled to Romania, along with Smigly-Rydz. The previously friendly relations between the two states had encouraged the Poles to seek refuge in Romania, but the following day – as a result of intense German diplomatic pressure on Romania – they were interned and transported deep into the interior of the country.
German withdrawal problems
The sudden arrival of the Red Army marching eastwards caused particular problems for the German army. The Nazi-Soviet Treaty had agreed to divide Poland along the Narew-Vistula-San river line, and German forces were instructed to withdraw slowly to that line. But on 17 September, much of the German army was still engaged in reducing remaining pockets of Polish resistance east of this line, and to withdraw would enable the Poles to retreat to the sanctuaries of Hungary and Romania.
A further problem caused by the sudden arrival of the Red Army was that soldiers had problems distinguishing friend from foe, and on a number of occasions German and Soviet troops shot at each other with loss of life. These incidents were relatively minor, however, and for the most part the German withdrawal was an orderly operation. A certain degree of fraternisation occurred between the German and Soviet forces, and a number of such incidents were recorded by the propaganda units of both sides. At BrestLitovsk, on 22 September, a combined parade of German and Soviet armoured units was followed by a banquet attended by the two leading commanders from both armies, Generals Guderian and Kriwoschein.
The German withdrawal decision was potentially more difficult for the Fourteenth Army in southern Poland, which had to prevent Polish forces streaming south towards Hungary and Romania. The old fortress city of Przemysl had been invested by the Germans on 10 September (holding out until 15th), while the bulk of the Fourteenth Army pressed on towards Lwow, the last remaining focus of Polish resistance. On the 12th, the German 1st Mountain Division reached the city, but the degree of resistance they encountered forced the Germans to begin a controlled besieging operation. The Zboiska heights dominated Lwow, and on the 13th the Germans fought a hard battle to secure this key position, the city being surrounded on the following day.
The siege was still in progress when, on 20 September, Rundstedt ordered the Fourteenth Army to abandon the reduction of Lwow to the Red Army and retire westwards. Rather than be captured by Soviet forces, however, the Lwow garrison suddenly surrendered to the surprised Germans as they were preparing to leave.
In 36 days of intense warfare, the Polish army had been destroyed as a fighting force. Fatal casualties amounted to 66,300 men, with 130,000 wounded. The Germans claimed to have captured nearly 700,000 Polish troops, but this figure was almost certainly too high, a total of around 400,000 being more likely. Perhaps as many as 200,000 Poles were taken into captivity by the Soviet Union where many died, but where others managed to get out via the Middle East (and fight with the British). Approximately 100,000 Polish troops had already escaped the German-Soviet net in September 1939 by fleeing to Hungary, Romania and Lithuania.
According to revised German figures, their army suffered 10,600 killed, 30,000 wounded and 3400 missing during the campaign. During September, 217 German tanks had been destroyed, but wear and tear had further reduced the fighting strength of the mechanised divisions. The XIX Corps, which had been withdrawn to East Prussia towards the end of September, was completely immobilised for a while in order to overhaul its battered vehicles, which included tanks, armoured cars and trucks. The Luftwaffe lost 285 aircraft destroyed, with a further 279 damaged beyond repair (Poland lost 284 aircraft in combat and 149 from other causes).
Poland had been partitioned three times by Prussia, Austria and Russia in the late 18th century. In 1939, Poland experienced a fourth partition. To finalise the details, Ribbentrop flew to Moscow, and on 28 September he signed the ‘German-Soviet Treaty of Delimitation and Friendship’. In this agreement, Germany accepted the inclusion of Lithuania into the Soviet sphere of influence, while, by way of compensation, Germany extended its control over Polish territory further east to a new line on the River Bug. Although the Germans wanted access to oil, Stalin refused to surrender the territory east of the River San, which included Lwow and the oil fields of Drohobycz and Boryslaw. Both sides were generally pleased with the new agreement, however, and Stalin was not slow in exercising his ‘rights’ over the Baltic States, which came under pressure to accept Soviet control. Even before the Baltic States’ formal annexation in August 1940, Stalin had turned towards Finland to demand territorial concessions along the Soviet-Finnish border. The Finnish refusal to accept the Soviet demands led to war on 30 November 1939, and while the Red Army suffered heavy losses in the initial stages of the campaign, superior numbers forced the Finns to accept a settlement in March 1940.
Mistreatment of the Poles
The old animosity that both Germans and Russians felt towards the Poles was now given full expression. One of the protocols of the new German-Soviet Treaty declared: ‘The two parties will tolerate in their territories no Polish agitation affecting the territory of the other party. They will suppress in their territories all beginnings of such agitation and inform each other concerning suitable measures for this purpose.’ In this, if in nothing else, the Germans and Soviets were united.
Over the next six years the people of Poland would suffer terribly. Both the German and Soviet authorities deliberately set about exterminating the political and social elites of Polish society. Following closely in the wake of the German army, SS extermination squads began to carry out summary executions of those declared ‘undesirable’ – as early as 25 October 1939,16,376 Poles had already been executed by the German police and armed forces. People living within areas under Soviet control experienced similar treatment. If the Polish campaign had been a triumph for the Wehrmacht, then for the people of Poland it represented the beginning of a living hell.