After the outbreak of World War I he fought with his unit against the Imperial Russian Army in the battles of Rzeszów, Dukla Pass and Gorlice.

In November 1918, after Poland regained its independence Sosabowski volunteered for the newly formed Polish Army, but his wounds were still not healed and he was rejected as a front-line officer.

Promoted to lieutenant colonel, in 1928 he was finally assigned to a front-line unit, the 75th Infantry Regiment, as commanding officer of a battalion.

Shortly before the German invasion of Poland started his unit was moved from its garrison in the Warsaw Citadel to the area of Ciechanów, where it was planned as a strategic reserve of the Modlin Army.

Instantly upon arrival, Sosabowski was ordered to man the Grochów and the Kamionek defensive area and defend Praga, the eastern borough of Warsaw, against the German 10th Infantry Division.

Despite constant bombardment and German attacks repeated every day, Sosabowski managed to hold his objectives at relatively low cost in manpower.

On 29 September, shortly before the Polish forces left Warsaw for German captivity, General Juliusz Rómmel awarded Col. Sosabowski and the whole 21st Infantry Regiment with the Virtuti Militari medal.

Upon his arrival in London, Sosabowski turned up at the Polish General Staff and was assigned to 4th Rifles Brigade that was to become a core of the future 4th Infantry Division.

In September 1943, Lieutenant-General Frederick Browning proposed that Sosabowski reform his unit into a division and fill the remaining posts with British troops.

The Brigade was ready to be dropped by parachute into Warsaw to aid their comrades from the underground Polish Home Army, who were fighting a desperate battle against overwhelming odds.

[3] Despite Sosabowski's concerns and warnings from the Dutch Resistance that two SS Panzer Divisions were in the operations area, Market Garden proceeded as planned.

He proposed that the combined forces of XXX Corps, under Lieutenant-General Brian Horrocks, and the Polish 1st Independent Parachute Brigade should start an all-out assault on the German positions and try to break through the Rhine.

This plan was not accepted, and during the last phase of the battle, on 25 and 26 September, Sosabowski led his men southwards, shielding the retreat of the remnants of the 1st Airborne Division.

Casualties among the Polish units were high, approaching 40%, and were at least in part, the result of Lieutenant-General Browning's decision to drop the paratroops 7 kilometres from the bridge at Arnhem.

[citation needed] However, on 14 October 1944, Montgomery wrote another letter, this time to the British commanders, in which he scapegoated Sosabowski for the failure of Market Garden.

[citation needed] Sosabowski was accused of criticizing Montgomery, and the Polish General Staff was forced to remove him as the commanding officer of his brigade on 27 December 1944.

[citation needed] In the opinion of historian Michael Alfred Peszke, "The worst thing that a subordinate can do is to question orders and to be proved right."

Consequently, Churchill coerced Polish Prime Minister Stanisław Mikołajczyk into cooperating with Stalin's disciples, or else risk losing Britain's support for the remainder of the war.

The information came on 16 October in a telegram to Field Marshal Sir Alan Brooke, the Chief of the Imperial General Staff, who was present in Moscow as Churchill's military advisor.

Churchill could use this claim to put more pressure on Mikołajczyk to cooperate, because it could be argued that one of his most valuable assets, Sosabowski's elite brigade, was no longer useful to the Allied war effort.

[9] In addition, war correspondents spoke highly of the Polish contribution to Market Garden in the same period as Montgomery was expressing his negative experiences, via Field Marshal Brooke, to Prime Minister Churchill.

Like many other Polish wartime officers and soldiers who were unable to return to Communist Poland on pain of repercussions including death or disappearance, he settled in West London.

In The Hague, on 31 May 2006, Queen Beatrix of the Netherlands awarded the Military Order of William to the Polish 1st Independent Parachute Brigade.

[15] In part this was the result of a Dutch TV documentary depicting the brigade as having played a far more significant role in Market Garden than had been hitherto acknowledged.