Everything in the airplane was from out on the frontier limb, including the material from which it was made. A special alloy of magnesium and radioactive thorium-232, “mag-thor” or HK-31, was used, giving the airframe superior strength and temperature endurance for supersonic flying. The thorium content gave the airplane a bigger radiation signature than the thermonuclear device it carried, but it was harmful only if ingested. There was no room in the fuselage, thin as a supermodel, for a bomb bay. The big, fat bomb was carried along with jet fuel inside the detachable auxiliary gas tank, slung underneath.[199] It was not easy to fly, and, despite all the electronic help, the three-man crew was kept busy. Altogether, the surfeit of innovation contributed to the accidental loss of 26 B-58s, over 22 percent of the 116 that were built. In ten years of flying around with bombs on board, only one nuclear-weapon incident occurred on a B-58, when in 1964 a fully loaded Hustler slid on ice at Bunker Hill AFB, Indiana, while trying to turn onto the runway. The landing gear hit a concrete electrical box, the plane caught fire, and the five nuclear weapons on board were destroyed.
With this combination of complex weapons, tricky flying machines, and men working under stress, packed down by a towering bureaucracy and a constant threat of war breaking out, it is a wonder that civilization survived. Somehow, the safety systems on both sides of the Cold War seem to have functioned well. But it was still not foolproof.
The era of nuclear-weapon accidents began on February 13, 1950, when B-36 no. 44-92075 was flying between Air Force bases Carswell in Texas and Eielson in Alaska on a simulated combat mission. The weapon on board was an MK-4. Its removable composite plutonium-uranium capsule, type 110, was replaced with a lead dummy for training purposes. Aside from the core, it was a complete MK-4, all 10,850 pounds and looking like a black teardrop with fins. The plane was an early, Model B example of the B-36, built before the jet engines were added.
The bomber had flown six hours when it started to ice up. It was at 12,000 feet, and the ice forming on the wings and propellers was so heavy, the crew could not climb out of the icing conditions. After a while, three engines caught fire. The Pratt & Whitney rotary engines were highly advanced for the time, but they were piston engines, mounted backwards on the wings. Usually, rotary engines were mounted with the carburetors in back, warmed by the hot air streaming through the cooling fins on the engine cylinders, but in this case the carburetors were in front, sucking in cold air with no advantage from engine heat. Ice formed on the air intakes, restricting the airflow and causing the fuel-air mixture to become mostly fuel. Raw aviation gas started to blow out the red-hot exhaust pipes, and fire was inevitable. With half the engines out, the lifetime of the airplane was severely limited.
The crew turned the bomber out over the Pacific Ocean, cranked open the bomb bay doors, and released the MK-4. It whistled off into the darkness, fell 5,000 feet, and made a bright flash as its airbust fuse detonated the implosion charge. Five seconds later, the shock wave rattled the bones of the big, crippled plane. The crew turned the aircraft around and made for land, steadily losing altitude. As soon as they saw Princess Royal Island below them, the crew bailed out. The copilot took one last look at the plane as he rolled over before his chute opened. He saw a brilliant blue-white stream of flame from an engine extending back to the tail. It appeared that the engine’s magnesium heat exchanger had caught fire, and he guessed that the plane would self-destruct in a ball of flame any minute now as the fuel tanks ignited. Every crew member made it back alive.
Abandoned, the B-36 leveled out and turned due north. It flew inland for 200 miles, finally running out of gas and crashing on the remote, perpetually snowed-in Mount Kologet, British Columbia.[200] The MK-4 presumably blew itself to unrecoverable smithereens using the implosion explosives, without causing a full-nuclear event.
The next loss of an MK-4 nuclear weapon occurred two months later, when a B-29 carrying it took off at night from Kirtland Air Force Base in New Mexico. Taking off on Runway 8 at Kirtland was tricky, in that you had to make a right turn as soon as possible or you would run into the mountain at the Monzano Base Weapons Storage Area. The pilot, Captain John R. Martin, failed to execute the turn promptly and flew right into the hill three minutes after takeoff. The plane exploded and killed all thirteen people on board. The MK-4 was broken to pieces, with some of its explosive segments scattered and burned up in the gasoline fire. The capsule, stored separately in its birdcage, was recovered along with four spare detonator assemblies in carrying cases. The mission had been to ferry the bomb and some personnel to Walker Air Force Base in Roswell, New Mexico. For decades after the crash you could still see pieces of the plane glittering in the sun on the west slope of the mountain if you knew where to look.
Three months later, a B-50, an upgrade of the aging B-29 bomber from World War II, was on a secret mission to transport an MK-4 nuclear weapon to a base in the United Kingdom. Just to be perfectly safe, the capsule was being transported on a separate flight. It was a clear day. After takeoff from Biggs Air Force Base in Texas, the plane was seen in a spiraling descent over Lebanon, Ohio, at about 2:54 P.M. local time. There were no parachutes visible. It stalled briefly at about 4,000 feet, then fell into a spin to the right and flew straight into the ground. The high-explosive components of the MK-4 went off on contact, and the bomb, the airplane, and the 15 men on board were obliterated. The cause of the crash was never determined. The separate plane carrying the nuclear capsule landed without incident.
A month later, on August 5, 1950, another B-29 transporting an MK-4 without nuclear capsule to Anderson Air Force Base, Guam, from California experienced two runaway propellers and landing gear that would not retract on takeoff. The pilot turned the plane around to try an emergency landing, but the left wing touched ground and the plane crashed, killing 12 crew members. Twenty minutes later, as the twisted wreckage burned from its full load of aviation gasoline, the atomic bomb’s implosion explosive went off, and the shock wave, heard 30 miles away, wiped out a nearby trailer park, killing or injuring 180 military, civilians, and dependents. Among the fatalities in the airplane was Brigadier General Robert F. Travis. The Air Force base, Fairfield/Suison, was renamed Travis Air Force Base to honor him.
The year 1950 was not good for MK-4 nuclear weapons.[201] Another one was ditched over the St. Lawrence River near St. Alexander-de-Kamouraska, Canada, from a B-50 on November 10. It was missing the nuclear capsule, but it still blew up into a million pieces when it hit the water. It was one of 15 MK-4s being air-transported from Canadian Force Base Goose Bay, Labrador, back to Arizona at the end of a six-week deployment beginning on August 26, 1950. The reason for having 15 nuclear weapons staged in Canada at that time is not clear.
Things were quiet until 1957, when on May 27 a late-model B-36J was ferrying a deactivated MK-17 from Biggs Air Force Base in Texas back home to New Mexico. The MK-17 was a thermonuclear weapon with a 15-megaton yield, made very complicated by its use of a cryogenic deuterium-tritium mixture for explosive fusion. It had been pressed into emergency service while a lighter bomb using solid-state lithium-deuteride was developed. The B-36J had lined up for the landing on Runway 26 at Kirtland and was coming in slow at 1,700 feet.
It was a written procedure at the time to pull out the locking pin on the bomb release before landing in a strategic bomber. It was designed to prevent any chance of an accidental drop while in flight, but if the landing started going bad, the base wanted you to jettison the bomb before you crashed and made a big crater in the runway. The locking pin would make a hasty decision to deploy impossible, so the captain always sent a man who was not needed for anything else to the bomb bay to disengage the pin and allow a drop if necessary. The captain, Major Donald F. Heran, sent a co-observer back to the bomb bay to pull it.
199
This cohabitation of fuel and bomb in the MB-1C pod did not last long. Predictably, there were unsolvable problems with fuel leaking into the bomb and out of the pod. This design was replaced with the TCP (two-component pod), in which either the fuel tank or the bomb could be dropped independently. The introduction of the 1-megaton MK-43 aerial bomb in April 1961 made this possible. The B-58 could carry four of these weapons along with the TCP. The MK-43 was interesting in that the wrenches, H745 and H1210, used to arm it were stored in a neat compartment recessed on the left side of the bomb.
200
You can find the crash site using Google Earth. Just look for Mount Kologet, and the crash site is indicated on the Wikipedia layer. A B-36 was a lot of metal, and although scroungers have carried off some interesting pieces, there is too much splattered all over the mountain to ever clean up completely. The wreckage was found and identified on September 3, 1953, by a team of Air Force investigators who hiked in on foot. Identification was confirmed by the number 511 found on the nosewheel door. The site was relocated accidentally by civilian surveyors in 1956, but they did not think to tell anyone about it. Finally, in 1997 one of them mentioned it to somebody and word got around. Both the United States and the Canadian Departments of Defense immediately launched expeditions just to look at it. The original discovery document, a single teletype page having the lat/long of the site, had long since disappeared into the filing system. Since the 1997 expedition, the location has been public knowledge.
201
An odd incident, assumed to be an accident, occurred on March 10, 1956, somewhere over the Mediterranean Sea. A B-47 engaged in Operation Chrome Dome was ferrying two nuclear capsules to an overseas air base. It was scheduled for an in-flight refueling 14,000 feet over the Mediterranean. It never showed up. The airplane, its crew, and the two capsules simply vanished. Not a trace has ever been found.