Boeing XB-52 Stratofortress
The XB-52 is the very first prototype for the B-52 Stratofortress. It has first flown in 1952 which later became operational in 1954, tagged by the US Air Force as B-52 Stratofortress.
The B-52 Stratofortress as a predecessor of B-47, was utilized by US Air Force for their, long range bombing missions. During the cold war era, it used to carry nuclear weapons where it was later commonly called BUFF or Big Ugly Fat Fucker.