|English: The guided bomb unit-43/B Massive Ordnance Air Blast bomb prototype is shown moments before impact. The detonation created a mushroom cloud that could be seen 20 miles away. (Photo credit: Wikipedia)|
Good writeup from JustSecurity, part of which is included here.
Read rest of storyThe Massive Ordnance Air Blast Weapon (MOAB, known informally as the “Mother of All Bombs” and formally as the Guided Bomb Unit, or GBU, 43/B) has attracted a great deal of attention since it was dropped on ISIS fighters in eastern Afghanistan on 13 April. Unfortunately, discussion of the attack has been hobbled by a lack of understanding as to the nature of the weapon and the uses for which it was designed, as well as the tendency to discuss it by reference to nuclear weapons. In this article, we hope to add some needed granularity to the analysis of the attack by describing the MOAB and its purpose. We conclude by highlighting the international humanitarian law issues implicated by the attack.Developed in a relatively short time during 2003 with a view to use in Iraq, the MOAB was never employed in that conflict. The intent was to use it against large formations of troops or hardened above-ground bunkers. It was also intended for “psychological operations” targeting enemy morale, both by virtue of the size and extent of the resulting blast and the fact that it creates a large mushroom cloud resembling that of a nuclear detonation. Thus, it was seen as a particularly useful weapon for “shock and awe” type tactics.The MOAB is huge by conventional bomb standards. Weighing in at approximately 11 tons, it contains 18,700 lbs. of H-6 explosive, which was originally developed for underwater explosions due to its low sensitivity to shock and stable storage characteristics. This is the largest quantity of explosive in any non-nuclear weapon in the US inventory (although there are larger weapons by weight, they contain less explosive due to having heavier casings designed to penetrate targets). By way of comparison, the frequently-used Joint Direct Attack Munition (JDAM) comes in at launch weights of between roughly 500 lbs. and 2000 lbs.Although the military has recounted “kicking it out of the back door” of the MC-130 aircraft, which suggests a “barrel-bomb” approach to employment, the MOAB actually is a guided munition. After leaving the aircraft, a parachute attached to the MOAB deploys. The weapon subsequently detaches and is guided to a pre-determined target by GPS (satellite) and onboard avionics. Thus, it differs from its predecessor, the obsolete BLU-82 “Daisy Cutter” bombs developed for use in Vietnam. Daisy cutters were unguided “dumb” bombs that created large blasts areas in order to clear sites that could subsequently be used for helicopter landing zones. They saw some limited use in both Iraq and Afghanistan, including against cave complexes, until 2008.The MOAB must be distinguished from the class of volumetric weapons, such as thermobaric weapons and fuel-air explosive weapons that have been used against fighters within cave complexes in Afghanistan. Those use various means to create a cloud of burning particles with a wide blast radius and intense fireball. When employed in a confined area, such as caves, thermobaric weapons can create a powerful vacuum as a secondary effect that adds to their lethality.The MOAB is a conventional explosive weapon. It results in an initial fireball from the explosion and a subsequent pressure wave caused by the creation of large quantities of gases at high temperatures. The MOAB is an air burst weapon, that is, it detonates above the ground. This allows its destructive energy to dissipate over the widest possible surface area rather than being absorbed by the ground impact or reflected upwards. It can be used both to demolish surface targets and as an anti-personnel weapon. The effects are similar to any standard high explosive weapon, but the size of the blast radius (reported to be approximately 1 mile) is what marks the MOAB apart from smaller munitions.