The B-36 was an immense aircraft in every dimension and one of the last of the piston driven bombers. Designed as a long distance heavy bomber capable of carrying a huge bomb load or the nuclear bombs of the period, it went through numerous re-designs and modifications. The first B-36A was built in early 1947 and flew for the first time on August 28, 1947. The models B and C soon followed and were found wanting for one reason or another, mostly because the Air Force and the Government's Department of Defense could not arrive at a long-term agreement about what they wanted. Some wanted the B-36 to fill the gap before the B-52's would be delivered; others thought it was not needed at all and still others changed their minds every month or so.

The early versions of the B-36 had been criticized for insufficient maximum speed and for a too-long takeoff run. On October 5, 1948, Convair proposed that these problems could be addressed by fitting two pairs of turbojets in pods underneath the outer wings. These turbojets would be used for takeoff and for short bursts of speed during the bombing run and would have only a minimal effect on the range. These changes resulted in the B-36D version.

The B-36D featured two pairs of General Electric J47-GE-19 turbojets in pods underneath the outer wings to assist the six R-4360-41 engines. These pods were quite similar to those fitted underneath the inner wing of the Boeing B-47 Stratojet. The jet engines increased the maximum speed to 435 mph and the ceiling to more than 45,000 feet. In addition, they reduced the takeoff run by almost 2000 feet.

The first true production B-36D flew on July 11, 1949. The first B-36Ds were accepted by the USAF in August of 1950 and were initially sent to Eglin AFB for testing. By June of 1951 26 B-36Ds had been delivered. The last B-36D was accepted in August of 1951. A total of 81 B-36Ds were delivered to the USAF, 22 built as B-36Ds from the start and 59 others were converted from B-36Bs.

The model D was fitted with snap-action split bomb-bay doors as opposed to the sliding type doors fitted to the preceding B-36As and Bs. These doors could open and close in only two seconds and were extremely hazardous to ground crew. The maximum bomb load was 86,000 pounds, consisting of two 43,000-pound bombs. Smaller alternative loads consisted of three 22,000 pound bombs, four 12,000-pound bombs, 12 4000-lb bombs, 28 2000-lb bombs, or 132 500-lb bombs. Such loads were not equalled until the "Big Belly" B-52D modifications during the Vietnam War.

The B-36D had six 3500 Pratt and Whitney Wasp Major radial engines mounted facing rearwards on the trailing edges of the wings, plus four 5200 lb thrust GE J47 turbo jets. It had a maximum speed of 439 mph at 32,120 feet with a cruising speed of 225 mph and a range of 7500 miles. Its service ceiling was 45,200 feet. To clear a 50 ft obstacle on take-off, it needed 5685-ft runway. Empty it weighed 161,370 lbs., combat weight of 250,000 lbs., with an absolute maximum lift off weight of 370,000 lbs.

The B-36D's wingspan was 230 feet, its length 162 feet 1 inches, with a height of 46 feet 8 inches and a wing area of 4772 square feet. For armament it carried two 20-mm cannon in each of six retractable, remotely controlled fuselage turrets, plus a tail turret and a nose mounting.

The B-36D had a crew of 15: commander, two pilots, two engineers, navigator, bombardier, two radio operators and an observer forward (the first radio operator handled ECM while the second radio operator, the copilot and the observer operated the three forward turrets. The rear compartment accommodated five gunners, including one for the radar controlling the tail turret.

On January 16, 1951, 6 B-36Ds were flown from Carswell AFB to the United Kingdom, landing at RAF Lakenheath after having staged through Limestone AFB in Maine. The flight returned to Carswell on January 20. This marked the first time that B-36s had flown outside US territory. A flight to French Morocco was made on December 3, when 6 B-36s of the 11th Bombardment Wing landed at Sidi Slimane, having flown non-stop from Carswell AFB.

Gradually, most of the problems with the B-36 were identified and corrected. An early major B-36 problem was leakage in the fuel system. In addition, the electrical system was unreliable and caused frequent fires. Improved containers and better sealants reduced fuel tank leakages. Changes in the electrical system reduced fire hazards during ground refuelling operations. Landing gear and bulkhead failures were almost totally eliminated.

However, even by October of 1951, the B-36D's defensive armament system was still performing poorly. In April of 1952, the Air Force ordered a series of gunnery missions to see if the cause of the failures could be determined. This test was completed in July. The K radar system was found difficult to operate and maintain and the training for the gunners was found to be inadequate.

In August and September of 1953, B-36s of the 92nd Heavy Bombardment Wing completed the first mass flight to the Far East, visiting bases in Japan, Okinawa and Guam. This flight took place shortly after the hostilities ended in Korea and was an effort to demonstrate US willingness to maintain operations in the Far East. On October 15 and 16, 1953, the 92nd Heavy Bomb Wing left Fairchild AFB in Washington for a 90 day deployment to Guam. This was the first time an entire B-36 wing had been deployed overseas.

The B-36 flew fairly well on just four or even three piston engines, so it was common practice to shut down some of the engines during cruise. The turbojets were normally used only for speed dashes over the target area or for takeoff. Several B-36Ds were modified as lightweight, high-altitude aircraft by being stripped of all armament except the tail turret making it possible for the B-36 to reach altitudes in excess of 50,000 feet. 26 B-36Ds were built from scratch. In addition, some 64 B-36Bs were converted at Convair's San Diego facility to B-36D configuration. The last B-36Ds were taken out of service in 1957.