Mark 17 Thermonuclear Bomb The MK-17 was the first operational USAF thermonuclear "H-Bomb" (The "H" refers to the hydrogen which was fused under intense heat conditions to produce unprecedented energy yields). The MK-17 was carried by B-36s and was in service from 1954 until 1957. By today's standards, it was extremely large and heavy. It had a casing 3 1/2 inches thick, a length of 24 feet 10 inches, diameter of 5 feet 2 inches and a loaded weight of 41,400 pounds. When the bomb was test-dropped, pilots said the bomber might soar upward several hundred feet, having been lightened of such a load. The MK-17 had an explosive force (yield) in the megaton (one million tons of TNT) range. A 64-foot ribbon chute stabilized the MK-17 bomb when dropped and slowed its descent, giving the bomber greater time to escape the area of detonation. (Note: a plastic cover has been added to protect the parachute while on display.) Miniaturization has been one of the major advances to affect the size of nuclear weapons from the 1950s until today for size is no longer an accurate gauge of a weapon's yield. Click here to return to the Cold War Gallery.