The Lightnings' engines were troubled by the addition of alcohol used as an anti-knock compound in their fuel supply; a British war economy solution which caused problems with water condensation on the ground and fuel line icing at altitude. Another British attempt to correct fuel composition caused lead metal deposits to coat cylinders and foul plugs throughout the squadron. The -H series Lightnings did not have adequate cooling for extended high-power usage, as their engine development had outstripped the cooling capacity of the integral intercooler which ran through the wing's leading edge. Pilots were instructed to restrict their periods of highest engine power to defined time limits, but many did not. As a result of these various influences, the Group's Lightnings suffered a high rate of attrition. Nevertheless, 55FG P-38H pilots provided cover for missions against aircraft plants during Big Week in February 1944. Lt. Col. Jack Jenkins led the group on 3 March 1944, when they became the first Allied fighters to reach Berlin on an escort mission.