The US Air Force has commissioned Boeing to produce a new batch of GBU-57 Massive Ordnance Penetrators (MOPs), the 13,600kg (30,000lb) mega-conventional bombs used for burrowing deep inside fortified bunkers and detonating.

A nearly $21 million contract awarded to Boeing on 8 February buys an unknown quantity of the weapon. The contract award notice says Boeing will produce “massive ordnance penetrators”, with the plural indicating more than one. The Air Force expects the deliveries from Boeing before 31 July 2020.

Boeing declined to release further details about the quantity of the order.

The MOP entered development in 2004 under a project sponsored by the Defense Threat Reduction Agency (DTRA). It was turned over to Air Force as a quick reaction capability in 2010, then assigned to the Global Strike Command in 2015, according to military records.

The weapon boasts several times the mass of the 2,270kg BLU-109 penetrator, enabling the MOP to attack a new class of hardened bunkers.

The MOP has been integrated on the Boeing B-52H and the Northrop Grumman B-2A Spirit. Some analysts have speculated that the weapons bay of the Northrop B-21 will be sized to accommodate the USAF’s largest conventional weapon as well.

A USAF fact sheet says previous contracts acquired a stockpile of 20 GBU-57s through November 2015, but it’s not clear how many more have been added in the last two years.

Budget documents show the MOP inventory is receiving major upgrades. The air force has integrated an unspecified list of improvements since Fiscal 2014, yielding the improved ETR-III and ETR-IV versions of the weapon. The USAF also is working to integrate the anti-jam Code M GPS signal into the MOP.