[StrategyPage.com] Air Weapons: More MOP For Mister KimIn 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.