Recent events have bestowed international attention on a specialised type of munition of the United States Airforce called the MOAB.
Referred to as "Mother Of All Bombs" this is, however, the nickname given to this weapon, the correct abbreviation of this weapon is "Massive Ordnance Air Blast Bomb".
Designated as GBU-43/B by the United States Armed Forces, whereas GBU stands for Guided Bomb Unit.
It was designed and developed by the Air Force Research Institute and is currently being manufactured McAlester Army Ammunition Plant.
Currently the biggest non-nuclear weapon in the world with, with the Russian FOAB as second.

Basic specifications and intended purpose:

Total weight is 9.800 (921,000 lb) and the explosive component weighs in at 8.500 kg (18.700 lb) yielding an 11 tonnes blast yield.
The weapon is also guided by GPS(KMU-953/B GPS/INS) and deployed at high altitude protecting the C-130 from short range AA MANPADS.
It can only be dropped from a military transport aircraft the C-130 and variants, it uses a drogue parachute and cradle to extract from the C-130.
As a thermobaric weapon utilizes the oxygen from the surrounding area to create an intense heat and serves mainly to defeat soft targets.
Since it soaks up all the surrounding oxygen it will kill all life that is caught inside the blast radius.
While the MOAB can be used vs hard targets due to its massive explosive yield it is more an area of effect weapon.
It is not designed to penetrate but to explode right before hitting the ground to maximise the blast radius.
Because of the nature and design of the MOAB, it can also be used to clear an LZ in forest/jungle area or clear out mine fields.

History and deployment:

For the intended military application it was designed for the 2003 invasion of Iraq(Operation Enduring Freedom).
The main goal for the weapon was part of the shock and awe strategy as an anti-personnel weapon with a physiological effect.
MOAB is a area of effect weapon, a single weapon vs the multiple munitions dropped during carpet bombing.
It would have been useless in the Iraq war since not bunker complexes were used to defend an area during the Iraq invasion.
As mentioned above it requires a C-130 at high altitude what would make it extremely dangerous for the C-130 to fly into a hostile area.
The Iraq Army at the time had high altitude AA although most of them were taken out it was still possible some launch vehicles survived.
A common tactic for AA defence is to switch off the radar and switch it back on so it can not be engaged with radar seeking missiles used to counter AA defence.
Most likely the main reason it was not used at the time, to begin with, once engaged a C-130 has little chance vs semi-modern AA missile.

Fast forward to the war on terror it does however shine, the various terrorist factions do not have an air force nor do the have high altitude AA capabilities.
As an area of effect weapon that comes with soaking up the oxygen of the surrounding area, its niche is to target cave systems.
Carpet bombing mountain ranges and the case system in it will have little to no effect since there are multiple entry and exit points in a cave system.
The MOAB will soak up all oxygen and draw out oxygen from these cave systems due to the created vacuum where the MOAB explodes.
While the blast will have little to no effect especially at range inside a cave system the lack of oxygen will do the trick just fine.
Of course, anything outside in the open caught in the blast radius will be killed by the pressure of the explosion.
Another con when it comes to the MOAB the area is pretty much cleared of IED's but inside a cave system, one must be careful.
As the lack of oxygen will not temper with a trigger mechanism of an IED.

All in all the weapon was never designed for this but does the job very well, and it's intended design to same extend fails.
It is perfectly capable of clearing an area of tree's and mines but the 16 million price tag is a bit over the top for such a task.
For the Iraq war, it would have been an overpriced toy but it proves to be priceless in clearing out intricate cave systems.
It would take months and a large force to clear out a decent sized cave system what is also most likely rigged with IED's.
Offering a price tag equivalent in currency and not to mention the cost of human lives.
The conclusion is for conventional war this is a toy, for counter-terrorism this has defiantly a utility.

Paul Ripmeester