Boeing B-29/50 Superfortress
     The Boeing B-29 Superfortress was an aircraft of superlatives.  At the time it was built, It was the largest and most powerful airplane in the world.  It was designed in 1940 as an eventual replacement for the B-17 and B-24 in the European theater.  The prototype made its first flight on September 21, 1942.  It was soon decided that its long range would be more useful in the Pacific Theater where vast expanses of oceans separated bases from their targets.  It was first used to attack the Japanese homeland from bases in China. During the last two months of 1944, B-29s began operating against Japan from the islands of Saipan, Guam and Tinian.
     The airplane was loaded with incendiaries and used to firebomb Japan and mine its harbors, but it is best known as the first (and only) airplane to ever drop an atomic bomb. The "Enola Gay" dropped the first one on Hiroshima, Japan and "Boxcar" dropped the second on Nagasaki. 
    When SAC began in 1946, it's primary bomber aircraft was the B-29.  Although there were many in storage at Davis Monthan AFB, they were war-weary and antiqued.  The plane was greatly improved and soon new models, designated the B-50, began joining SAC inventory.
     The Enola Gay, a B-29 from the 509th Composite Group was the first aircraft to drop an atomic bomb.  .  The 509th became the nucleus of the Strategic Air Command.  The Enola Gay later participated in Operation Crossroads.  It is now owned by the National Air and Space Museum and is supposed to go on display at its new flight museum, at Dulles International Airport, near Washington, D.C.
All about the Strategic Air Command's first airplanes NEW  B-29 & B-50 Wing Poster

See the display models of the B-29