The M121 was a very large air dropped bomb used by the U.S. military during the Vietnam War. Originally developed from the British World War II-era Tallboy bomb to be dropped from the

Convair B-36 The Convair B-36 "Peacemaker" is a strategic bomber that was built by Convair and operated by the United States Air Force (USAF) from 1949 to 1959. The B-36 is the largest mass-produced piston-engined aircraft ever built. It had the longest wing ...

bomber A bomber is a military combat aircraft designed to attack ground and naval targets by dropping air-to-ground weaponry (such as bombs), launching torpedoes, or deploying air-launched cruise missiles. The first use of bombs dropped from an aircr ...

, it weighed 10,000 lb (4,500 kg) and contained an 8,050 lb (3,650 kg)

Tritonal Tritonal is a mixture of 80% TNT and 20% aluminium powder, used in several types of ordnance such as air-dropped bombs. The aluminium improves the total heat output and hence impulse of the TNT — the length of time during which the blast ...

warhead. Production of the M121 ceased in 1955, but stockpiles were retained until the Vietnam War.

Vietnam War

In December 1967, the

U.S. Air Force The United States Air Force (USAF) is the air service branch of the United States Armed Forces, and is one of the eight uniformed services of the United States. Originally created on 1 August 1907, as a part of the United States Army Signa ...

began a testing program to use large bombs for explosively clearing jungle areas for landing of helicopters. After tests in the United States, the

U.S. Army The United States Army (USA) is the land service branch of the United States Armed Forces. It is one of the eight U.S. uniformed services, and is designated as the Army of the United States in the U.S. Constitution.Article II, section 2, ...

began dropping the bombs using

CH-54 The Sikorsky CH-54 Tarhe is an American twin-engine heavy-lift helicopter designed by Sikorsky Aircraft for the United States Army. It is named after Tarhe, an 18th-century chief of the Wyandot Indian tribe whose nickname was "The Crane". The c ...

helicopters. Use of the helicopters was expensive, time consuming and inefficient due to the CH-54's limited

range Range may refer to: Geography * Range (geographic), a chain of hills or mountains; a somewhat linear, complex mountainous or hilly area (cordillera, sierra) ** Mountain range, a group of mountains bordered by lowlands * Range, a term used to i ...

. In October 1968, a

C-130 The Lockheed C-130 Hercules is an American four-engine turboprop military transport aircraft designed and built by Lockheed (now Lockheed Martin). Capable of using unprepared runways for takeoffs and landings, the C-130 was originally desi ...

crew A crew is a body or a class of people who work at a common activity, generally in a structured or hierarchical organization. A location in which a crew works is called a crewyard or a workyard. The word has nautical resonances: the tasks involved ...

from the 29th Tactical Airlift Squadron of the 463rd Tactical Airlift Wing flew a series of test drops while under the guidance of MSQ-77 radar controllers; additional test drops were made in December. In March 1969, the 463rd commenced Project Commando Vault, and

bomb A bomb is an explosive weapon that uses the exothermic reaction of an explosive material to provide an extremely sudden and violent release of energy. Detonations inflict damage principally through ground- and atmosphere-transmitted mechanica ...

drops became a regular occurrence. Besides clearing the jungle and preventing the ambush of helicopters that were approaching the

landing zone In military terminology a landing zone (LZ) is an area where aircraft can land. In the United States military, a landing zone is the actual point where aircraft, especially helicopters, land (equivalent to the commonwealth landing point.) In c ...

(the M121's blast diameter was 60 meters), the explosion also stunned the NVA or

Viet Cong , , war = the Vietnam War , image = FNL Flag.svg , caption = The flag of the Viet Cong, adopted in 1960, is a variation on the flag of North Vietnam. Sometimes the lower stripe was green. , active ...

personnel within 500 meters and revealed or destroyed

booby trap A booby trap is a device or setup that is intended to kill, harm or surprise a human or another animal. It is triggered by the presence or actions of the victim and sometimes has some form of bait designed to lure the victim towards it. The trap m ...

s in the landing area.Frankum, Roland Bruce. ''Like rolling thunder: the air war in Vietnam, 1964-1975''. Rowman & Littlefield, 2005. . Due to the bomb's weight and powerful effects, ordnance handlers would chalk mark the bombs as "

Excedrin Aspirin(acetylsalicylic acid) / paracetamol(acetaminophen) / caffeine is a combination drug for the treatment of pain, especially tension headache and migraine. It is sold in the US under the trade names Goody's Powder and Excedrin, although n ...

Headache #10,00x" where x was the sequence number of the bomb;John Brennan, Chris Evans. ''Vietnam War Helicopter Art: U.S. Army Rotor Aircraft''. Stackpole Books, 2012. . a reference to the well known (at the time) advertising campaign promoting the efficacy of the Excedrin brand of extra strength pain relievers. Use of the M121 to clear a jungle zone was a technical success, but the weapon did not satisfy

MACV U.S. Military Assistance Command, Vietnam (MACV) was a joint-service command of the United States Department of Defense. MACV was created on 8 February 1962, in response to the increase in United States military assistance to South Vietnam. MACV ...

's command requirement to clear a jungle area for five helicopters at the same time.Thigpen, Jerry L. ''The Praetorian STARShip: the untold story of the Combat Talon''. DIANE Publishing, 2001. Despite this, the United States continued to use the M121 to clear helicopter landing zones in the jungle until stockpiles were depleted while a more powerful bomb was developed for jungle-clearing purposes. The new

BLU-82 The BLU-82B/C-130 weapon system, known under program "Commando Vault" and nicknamed " Daisy Cutter" in Vietnam for its ability to flatten a section of forest into a helicopter landing zone, is an American conventional bomb, delivered from eith ...

, developed in 1969, entered service later in the Commando Vault program. Unlike the M121, which used

TNT Trinitrotoluene (), more commonly known as TNT, more specifically 2,4,6-trinitrotoluene, and by its preferred IUPAC name 2-methyl-1,3,5-trinitrobenzene, is a chemical compound with the formula C6H2(NO2)3CH3. TNT is occasionally used as a reagen ...

, the BLU-82 used a slurry mixture of

ammonium nitrate Ammonium nitrate is a chemical compound with the chemical formula . It is a white crystalline salt consisting of ions of ammonium and nitrate. It is highly soluble in water and hygroscopic as a solid, although it does not form hydrates. It is p ...

and powdered

aluminum Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. It h ...

. It had a slightly bigger blast diameter (80 meters).

Notes

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References

* https://web.archive.org/web/20070124145412/http://www.nationalmuseum.af.mil/factsheets/factsheet.asp?id=1013 * http://members.aol.com/samc130/bc130.html
Commando Vault report at University of Texas Vietnam War archive
Cold War aerial bombs of the United States Military equipment introduced in the 1950s