March 12, 2018:
In early 2018 the U.S. Air Force ordered another $21 million worth of their 14 ton deep penetrator bomb (the MOP or Massive Ordnance Penetrator, officially the GBU-57). Based on past purchases this would be 5-10 GBU-57s. Earlier purchases had included a lot of additional equipment as well as modifications to the B-2 bomber that is the only aircraft that carries this bomb. There is no official data on the number of MOPs the air force has because data on bombs used for tests and training are kept secret.
It is known that GBU-57 underwent modifications in 2013 and 2017 that required one of more of them to be used to ensure the mods had the desired effect. While the 2013 mods were apparently to increase penetration and effectiveness against Iranian underground facilities the 2017 mods apparently took the characteristics of North Korean (or even Chinese) underground facilities into account. The 2013 tests were apparently against an accurate replica of the main Iranian nuclear weapons development facility at Fordo. Some of the results of this test were distributed to American allies with the intention of sending a message to Iran. There is no indication that a similar message about GBU-57 performance was sent to North Korea after the 2017 tests.
The first eight GBU-57s were ordered in 2011 and by 2018 at least twenty had been purchased. In early 2013 the U.S. Air Force announced that because of unspecified improvements to the GBU-57. Seven of the first eight production model bombs were used for tests, which resulted in a classified list of tweaks to the existing design and these upgrades have been added regularly since 2011. All this apparently paid off during the 2013 test against the Fordo replica.
The GBU-57 contains 2.4 tons of explosives and costs $1.5 million each just for the bomb. Over $400 million has been spent on developing MOP, including continuing upgrades. Since 2011 most of the twenty B-2 bombers have been modified to carry these weapons (two bombs per B-2). This was apparently meant to send a message to Iran and North Korea. Other countries, like China, Russia and Pakistan, also have some important underground military facilities that could only be taken out by a MOP. But there the greatest number of such targets in Iran and North Korea.
The B-2 is important for the MOP because this bomb is meant to be used in an unexpected attack and by an aircraft that can slip past heavy air defenses. Thus even if there were deep bunkers in Somalia or Afghanistan you would not need a stealth bomber to deliver a MOP. The enemy in those countries have no way of detecting a high flying B-52, much less a stealthy B-2. But Iran and North Korea do have radars, and a B-2 could slip past those radars and take out the air defense system command bunkers, or any other targets buried deep. The United States has made it clear that any attack on North Korea would involve B-2s delivering MOPs.
The 6.2 meter (20.5 foot) long MOP has a thick steel cap, which was originally designed to penetrate up to 8 to 61 meters (26-200 feet) before exploding. The smaller number is for concrete (highest degree of hardness) or up to 61 meters of rocky earth. This was the original spec, which is now supposed to be improved. The 2013 modifications apparently addressed the fact that the then new Iranian nuclear facility (Fordo) was supposed to be buried beneath 90 meters of earth and rock.
The U.S. has not (officially) sold any GBU-57s to Israel, so any use of this bomb would have to be by American aircraft.