In December 1967, the
U.S. Air Force 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 began dropping the bombs using
CH-54 helicopters. Use of the helicopters was expensive, time consuming and inefficient due to the CH-54's limited
range. In October 1968, a
C-130 crew 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 drops became a regular occurrence. Besides clearing the jungle and preventing the ambush of helicopters that were approaching the
landing zone (the M121's blast diameter was 60 meters), the explosion also stunned the
NVA or
Viet Cong personnel within 500 meters and revealed or destroyed
booby traps in the landing area. Due to the bomb's weight and powerful effects, ordnance handlers would chalk mark the bombs as "
Excedrin Headache #10,00x" where x was the sequence number of the bomb; 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's command requirement to clear a jungle area for five helicopters at the same time. 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, developed in 1969, entered service later in the Commando Vault program. Unlike the M121, which used
TNT, the BLU-82 used a slurry mixture of
ammonium nitrate and powdered
aluminum. It had a slightly bigger blast diameter (80 meters). ==Notes==