Several pioneers developed early versions of dialysis machines during World War II when many injured soldiers and civilians suffered kidney damage and died. In 1937, a young Dutch physician, Willem Kolff, working in Groningen, Holland, had already put together a crude dialyzing machine and worked to refine it. After the Germans occupied the Netherlands in 1941, Kolff moved to Kampen where, in spite of wartime shortages, he constructed a dialysis machine using cellophane tubing and beer cans. He first used his device on a human patient in March 26, 1943 and, although all but one of the 15 patients he treated from 1943 to 1944 died, he persevered. By the end of the war, Kolff had refined his machine and began to promote its use, bringing dialyzers to The Hague, Amsterdam, and London.