Affectionately known as "the Jug", the P-47 was a heavy (7-ton) fighter for its time. Designed as an interceptor, it found its true role as a hard-hitting ground-attack aircraft. Its great structural strength and massive radial engine could withstand damage better than that of in-line engine fighters like the P-51and P-38. In March 1942 the first production models started coming off the assembly line, and in January 1943 the 56th Fighter Group was the first to make the new fighter operational, with the 8th Air Force based in Great Britain. Production really hit its stride with the P-47D, which was the largest series. The P-47D had a more powerful engine at high altitude and a heavier bomb load. With drop tanks, the P-47 could escort bombers as far as Berlin. These Thunderbolts were built in several production lots and with a host of designations.