The CBU-55 was a cluster bomb Fuel Air Explosive that was developed during the Vietnam War, by the United States Army, and was used only infrequently in that conflict. Unlike most incendiaries, which contained napalm or phosphorus, the 750 pound CBU-55 was fueled primarily by propane. Described as a "the most powerful non-nuclear weapon in the U.S. arsenal," the device was one of the more powerful conventional weapons designed for warfare.
The device had three main compartments, with propane, a blend of other gases, perhaps chlorine triphospate, or another oxidizing agent, and an explosive.
The CBU-55 had two variations. The CBU-55/B consisted of 3 BLU-73A/B fuel-air explosive sub-munitions in a SUU-49/B Tactical Munitions Dispenser, and the CBU-55A/B had 3 BLU-73A/B sub-munitions in a SUU-49A/B dispenser). The SUU-49/B dispenser could be carried only by helicopters or low-speed aircraft, whereas the SUU-49A/B was redesigned with a strongback and folding tailfins, so that they could also be delivered by high-speed aircraft as well.
The first generation of the CBU-55 was used during the Vietnam War, but only in a test mode by US forces. In 1971, a team from the Air Force Weapons Center at Eglin Air Force Base brought test versions of the CBU-55 to Southeast Asia for testing on two lower speed attack aircraft, the A-37 and the A-1. In late 1971, the team worked with the 604th Special Operations Squadron A-37 pilots at Bien Hoa, SVN to fly a handful of combat test missions. In December of that year, that same team came to Nahkon Phanom Royal Thai Air Base (NKP) to do the same tests with the 1st SOS Hobos, flying the Douglas A-1 Skyraider. On Dec 2nd, 5th, and 8th, three two ship Skyraider sorties were flown, carrying four each of the CBU-55. The NKP test project officer and flight lead for these three missions, Capt. Randy Jayne, helped the Eglin team write up the test results, which were overall not positive. The unusual deployment sequence for the three propane canisters, and the fact that they fell under small parachutes highly susceptible to significant wind drift, made deliver accuracy and aircraft survivability (when releasing low enough to minimize that wind drift) questionable. Also, the very high drag characteristics of the CBU-55 canister, with its flat back end, severely limited the Skyraider's ability to carry other bombs, rockets, and CBU, a further negative issue. Although the Air Force chose, based on the Bien Hoa and NKP tests, not to deploy the weapon to the two combat units in theater, an inventory of the canisters was kept. By April 21, 1975, South Vietnam had largely been conquered by the military from the north. Earlier in the month, a single CBU-55 had been flown from Thailand to the Bien Hoa airbase. The senior military officer in Vietnam, Major General Homer Smith, cleared the way for the Saigon government to use the weapon against the North Vietnamese Army. A Vietnamese C-130 transport plane circled Xuan Loc at 20,000 feet (6,100 m), then dropped the bomb. The contents exploded in a fireball over a 4-acre (16,000 m2) area. Experts estimated that 250 soldiers had been killed, primarily by the immediate depletion of oxygen rather than from burns. The CBU-55 was never used again in the war, and South Vietnam's government surrendered on April 30.
(As the NKP test pilot noted above, and having observed both CBU-55 and other much larger propane fuel-air explosive weapons in Southeast Asia, I highly doubt that the C-130 drop cited here, of a "weapon shipped from Thailand", with the four acre area supposedly covered with high overpressure, was indeed CBU-55. I would assume, alternatively, that it was one of the much larger FAE weapons often dropped from transports like the C-130).
A second-generation of the CBU-55 (and CBU-72) fuel-air weapons entered the United States military arsenal after the Vietnam War, and were used by the United States in Iraq during Operation Desert Storm.
A foreign policy issue flared in the mid-1970's when the Israeli government sought to acquire from the US the small unused inventory of the original CBU-55 munitions. The debate was one of "inhumane" weapons, with the opponents of the transfer arguing that somehow, there was a distinction, in a very negative way, between using CBU-55 compared to HE bombs, other cluster munitions, napalm, etc. It was, to those of us who had actually flown combat with these various munitions, "a distinction without a difference".
- Spencer C. Tucker, Vietnam, UCL Press, 1999, p.185
- SBU/SBK to SXU - Equipment Listing
- CBU-72 / BLU-73/B Fuel/Air Explosive (FAE) - Dumb Bombs
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