One factor in this problem was developing tank technology. The German tanks that fought in North Africa were not the same ones that defended Western Europe. Panthers, in particular, were heavily armored and relatively fast. The 75mm guns of towed and mobile tank destroyer units that had defeated Panzer II and III tanks in North Africa found it more difficult to defeat Panzer IV and V tanks in Western Europe. This was a problem that affected the entire allied war effort and not just something which affected tank destroyers exclusively. Nevertheless, the only US weapon that could be counted on to defeat heavy German armor was the 90mm gun that was mounted on the M36 Tank Destroyer and M26 Pershing heavy tank, the latter being introduced too late to have any meaningful impact on the war. What this meant was that the towed battalions, supplied only with 75mm cannons, did not have the same advantage as the mobile battalions had when they were supplied with the 76mm and 90mm cannons of the M18s and M36s.