The most important American design of the war was the M4 Medium Tank, or "Sherman" in British service. The M4 Medium became the second-most-produced tank of World War II, and was the only tank to be used by virtually all Allied forces (thanks to the American lend-lease program); approximately 40,000 M4 Mediums were produced during the war. M4s formed the main tank of American, British, Canadian, French, Polish and Chinese units. The M4 was the equal of the German medium tanks, the Panzer III and Panzer IV, at the time it first saw service in 1942. The Red Army was supplied with about 4,000 M4s. The M4, although reliable and easy to maintain, was already outgunned by the time the US encountered the up-gunned and up-armored German medium tanks in Italy and Northern Europe (the Panzer IV and various German self-propelled guns) and by late 1943 the arrival of German Panther and Tiger I were even graver threats due to the range, accuracy and penetrating power of their main guns. While it is commonly believed that the Sherman had a tendency to explode catastrophically due to their use of petrol fuel, this is incorrect (almost all tanks used petrol in WWII, excepting Soviet tanks). The Sherman suffered from poor ammunition storage. Welded-on appliqué armor and water jackets were added to combat the problem. A U.S. Army study in 1945 concluded that 60–80 percent of the older dry-stowage and 10–15 percent of wet-stowage Shermans burned when penetrated. The Sherman gained grim nicknames such as "Tommycooker" from the Germans, who called British soldiers "Tommies".