Aviation History

The story of the B-52 Stratofortress that carried the Flashback Test Vehicle, the Nuclear Bomb Bigger than the Soviet Tsar Bomba

The Flashback Test Vehicle was larger by far than any other nuclear bomb in the US inventory at the time. It is a little bit bigger than the Soviet Tsar Bomba, the 50 megaton monster detonated in 1960 and designed to be 100 megatons in yield.

After it became operational in 1955, the B-52 Stratofortress remained the main long-range heavy bomber of the US Air Force during the Cold War, and it continues to be an important part of the USAF bomber force today. Nearly 750 were built before production ended in the fall of 1962.

The B-52 has set numerous records in its many years of service. On Jan. 18, 1957, three B-52Bs completed the first non-stop round-the-world flight by jet aircraft, lasting 45 hours and 19 minutes and requiring only three aerial refuelings. It was also a B-52 that made the first airborne hydrogen bomb drop over Bikini Atoll on May 21, 1956.

A B-52 was also modified to be the carrier of a mysterious “device” codenamed Flashback.

The Flashback nuclear test vehicle was so large it had to be partly suspended outside of the B-52 bomb bay.

As explained by Scott Lowther in his book Boeing B-47 Stratojet & B-52 Stratofortress Origins and Evolution, one truly effective way to be intriguing is to be mysterious. And the ‘Flashback’ modification of a of B-52C in the mid-1960s fits the bill perfectly.

In this case, the modifications made to the B-52 are not the interesting part, but the ‘Flashback Test Vehicle’ (FBTV) most certainly is. This was a payload built and carried by a B-52, a payload go intended to be dropped like a bomb. But was it a bomb? Was it a pure science experiment, or was it meant to lead to a practical device? After Flashback first emerged publicly around 2017, it remained shrouded in vagueness. Fortunately, information has begun to emerge.

The Flashback nuclear test vehicle was so large it had to be partly suspended outside of the B-52 bomb bay.

Flashback was part of a programme created after the signing of the Limited Test Ban Treaty in 1963. It was a way to rapidly build and demonstrate a high yield (50 to 100 megaton) hydrogen bomb in the event the Soviets violated the treaty, as they were likely expected to do. Flashback was a test of such a bomb… but without the actual atomic explosive, testing the associated hardware, ballistics and electronics. The bomb casing and other hardware would be tested and ready to go, with the fission/fusion explosive expected to be plugged in and ready to detonate within 90 days of the Soviet test.

January of 1965, the Flashback Test Vehicle was tested at Kirtland Air Force Base in New Mexico. These tests did not involve the dropping of a nuclear bomb which then detonated. Instead, the susceptibility of the Flashback device to electromagnetic emissions from the ARC-58 transmitter in the B-52 carrier aircraft and the device’s own telemetry transmitters was the point of the test. During the flight tests all high explosive and nuclear components were deleted and a simulator replaced the warhead. The Flashback device itself was large: large enough that in order to fit into the B-52 bomb bay the bomb bay doors had to be removed, and even then the device protruded from the belly of the aircraft. It was about 96 inches in di diameter and 297 inches long, not counting the protruding parachute pack or antennae.

The configuration of the Flashback Test Vehicle was distinct. At the front was a round-nosed cone that in Configuration and dimension closely – though not precisely – matched those of the Mark 6 re-entry vehicle from the Titan II ICBM. The use of a Titan II RV, if that is indeed what it is, was likely a matter of convenience and availability… although it could also potentially imply commonality with a Titan-delivered version of the high-yield warhead. A short cylindrical section followed, with a tapering tail section with three wedge-like tail fins. In the rear of the tail was a large Parachute package. The tail fins, it should be noted, are quite similar to the fins on large hydrogen bombs of the time. A number of antennae protruded from the rear of the device, presumably transmitters of onboard telemetry generated during a drop. The Flashback Test Vehicle and modified B-52C were shown in some poor-quality photos and some decent-quality wind tunnel model diagrams. These diagrams were used to provide a load good guide to shape and dimensions. The wind tunnel testing was conducted at the Cornell Aeronautical Laboratory in 1966; the testing was conducted for the Sandia Corporation, the designers of the Flashback Test Vehicle. Sandia Corporation operates Sandia National Laboratories, which is a premier nuclear to weapons ordnance engineering laboratory… i.e., they designed nuclear bombs. The wind tunnel models of the FBTV and the B-52 were built from aluminium and supplied to Cornell by Sandia. The tests involved determining the aerodynamics not only of the FBTV within the B-52’s bomb bay, but during a drop. It seems that the FBTV was planned for an actual drop from the B-52 in September of 1967 over Johnston Atoll as part of Operation Paddlewheel; whether that drop occurred is unknown.

This print is available in multiple sizes from AircraftProfilePrints.com – CLICK HERE TO GET YOURS. B-52H Stratofortress 2nd BW, 20th BS, LA/60-0008 “Lucky Lady IV”.

The Flashback Test Vehicle was larger by far than any other nuclear bomb in the US inventory at the time. It is a little bit bigger than the Soviet Tsar Bomba, the 50 megaton monster detonated in 1960 and designed to be 100 megatons in yield. It was not the sole configuration for a giant H-Bomb; there was also the Big Test Vehicle, a cylindrical device designed to fit within the B-52 bomb bay. This bomb was also on the scale of the Tsar in terms of yield.

The inclusion of a parachute pack shows that it was not going to be allowed to break the sound barrier on the way down; most likely it would begin deployment of the chutes almost immediately after being dropped. Sandia was the original promoter of the ‘laydown’ bomb, one which used a parachute to lower the bomb relatively gently to the ground; upon landing the bomb would not necessarily immediately detonate but would instead wait a set period of time. This, coupled with the retarded descent, would give the bomber aircraft the time needed to escape; for a bomb ai with a yield potentially measuring in the hundreds of megatons, the B-52 would need every second it could get to get away.

Boeing B-47 Stratojet & B-52 Stratofortress Origins and Evolution is published by Mortons Books and is available to order here.

Photo credit: U.S. Air Force

This model is available from AirModels – CLICK HERE TO GET YOURS.
Dario Leone

Dario Leone is an aviation, defense and military writer. He is the Founder and Editor of “The Aviation Geek Club” one of the world’s most read military aviation blogs. His writing has appeared in The National Interest and other news media. He has reported from Europe and flown Super Puma and Cougar helicopters with the Swiss Air Force.

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