Part 3 of 4 Parts (Please read Parts 1 and 2 first)
A large number of MOPs would be needed if the U.S. military were to attack the underground tunnel networks at the Natanz site because of how widely spread out these facilities appear to be. These facilities are now designed in sections with blast doors separating key sections. This means that if one area is hit, the other areas will not be impacted, or the damage will be drastically reduced to the entire facility.
Information is limited with respect to how many MOPs the Air Force has in its stockpile. Records show that twenty MOPs have been delivered by Boeing to the Air Force up to 2015. Additional MOPs have probably been delivered since then. This would include the GBU-57E/B variant, in operational inventory since 2016, and possibly the newest GBU-57F/B variant.
The MOP has been progressively improved over the years. There is no report on how many of the older variants have been retrofitted with modifications developed through the Enhanced Threat Response-IV and other upgrade programs.
It is also possible that the Air Force’s bunker busters may be able individually penetrate deeper below the ground than the Air Force has publicly admitted to date. Originally, the Air Force claimed that its MOPs could burrow down just sixty feet to destroy their targets. In 2007, this depth was adjusted to two hundred feet. It is likely that newer MOP variants, including the GBU-57E/B and GBU-57F/B, can reach a greater depth than the MOP variants available in 2007. The BLU-127C/B warhead has a “booster” in the front of the warhead. It is not clear if this constitutes a system to propel the section for added penetration or if it refers to an explosive charge accelerating the detonation of the main charge.
Other clusters of bunker busters could also be dropped on the known entry points of the underground facilities such as those in the Zagros Mountains. This maneuver could at least seal off the underground facilities temporarily. The GBU-57/B constitutes the largest bunker buster in the U.S.'s inventory. Smaller bunker busters such as the two-thousand-pound class BLU-109/Bs or BLU-137/Bs or five-thousand pound class GBU-28/Bs or GBU-72/Bs, or even GBU-57/Bs could be used for this purpose.
There are other ways to attack these facilities but with varying potential and risks. Deep penetrating, high risk commando raids on the ground could be used in an attempt to capture or severely damage nuclear development facilities. Cyber-attacks have been used in the past to slow down Iran’s nuclear program. However, these approaches would find it difficult to do serious physical damage to the facilities. There has even been discussion of irradiating the facilities and the land around them in order to deny access and use. Finally, nuclear warheads are the best bunker busters on Earth.
Please read Part 4 next