Was erstwhile (MG) James M. Gavin the highest-ranking US general officer?
Please see the question's title. I know that U.K. soldiers parachuted, but don't know if any Canadians, Polish did.
Gavin assumed command of the 82nd Airborne Division on August 8, 1944, and was promoted to major general in October. For the first time, Gavin would lead the 82nd Airborne into combat. On Sunday, September 17, Operation Market Garden took off. Market Garden, devised by Field Marshal Bernard Montgomery, consisted of an airborne attack of three British and American airborne divisions. The 82nd was to take the bridge across the Maas river in Grave, seize at least one of four bridges across the Maas-Waal canal, and the bridge across the Waal river in Nijmegen. The 82nd was also to take control of the high grounds in the vicinity of Groesbeek, a small Dutch town near the German border. The ultimate objective of the offensive was Arnhem.
In the drop into the Netherlands, Gavin landed on hard pavement instead of grass, injuring his back. He had it inspected by a doctor a few days later, who claimed that his back was fine, and so Gavin continued normally throughout the entirety of the war. Five years later, he had his back examined at Walter Reed Hospital, where he learned that he had, in fact, fractured two discs in the jump.