Churchill certainly knew of what was happening, he wrote in July 1944 "There is no doubt this is the most horrible crime ever committed in the whole history of the world, and it has been done by scientific machinery by nominally civilised men in the name of a great State and one of the leading races of Europe.". Bombing the train lines to Auschwitz was also considered, Churchill told Eden "Get anything out of the Air Force you can, and invoke me if necessary" (from the same link).

There were a number of requests submitted to the United States in June 1944, all were rejected in accordance with Allied policy not to have military resources used to deal with humanitarian issues whilst the war was ongoing, or as the War Department [put it] (https://books.google.co.uk/books?id=h-ewkTc29kYC&pg=PA79&lpg=PA79&dq=%E2%80%9Dfor+the+purposes+of+rescuing+victims+of+enemy+oppression.%E2%80%9D&source=bl&ots=8d9XRmeZ1q&sig=F2l9iKvqOBDcA5Uf2L8buj1pQIc&hl=en&sa=X&ved=0ahUKEwjU5sKM6erLAhVEWhoKHeB5A0UQ6AEIFDAA) in February 1944; "for the purposes of rescuing victims of enemy oppression."