WASHINGTON and LONDON — The US Department of State has cleared a major upgrade of attack helicopters for the UKnited Kingdom, potentially worth $3 billion.

The remanufacture of 50 UK WAH-64 Mk 1 attack helicopters to AH-64E Apache Guardian helicopters will "allow the United Kingdom greater interoperability with U.S. forces," according to a notice posted Thursday on the website of the Defense Security Cooperation Agency.

The UK Ministry of Defence confirmed in a statement Friday that it has also invited British helicopter manufacturer AgustaWestland to come up with a proposal to undertake work to bring the Apache helicopters up to the -E standard.

The assessment phase on the program ends in spring 2016. A decision on how the British government  intends to proceed in securing –E standard helicopters is expected in the summer of 2016 around the second quarter of 2016, after publication of the Strategic Defence and Security review towards the end of this year

The AH-64E configuration is the most advanced Apache design being used by the US Army, which plans to fully upgrade its fleet by the end of the decade. It features improved avionics, upgraded engines and new rotor blades.

The UK’s military "The United Kingdom will use the Apache helicopters to conduct various missions, including counter-terrorism and counter-piracy operations," reads the DSCA notice. "The materiel and services under this program will enable the United Kingdom to become a more capable defensive force and will also provide key elements required for interoperability with U.S. forces."

The prime contractor for the work will be Boeing at its Mesa, Arizona, facility, but Lockheed Martin and General Electric will also play a large part in the contract.

Among the wide range of equipment set to be stripped off the British helicopters for refurbishment and reinstallation on the airframes are the mast-mounted fire control radar, modernized target acquisition and designation sight, and pilot night vision sensors.

Other purchase options that have been looked at include a straight buy of new AH-64Es off Boeing's US production line and some degree of local assembly in the UK.

An MoD spokesman said: "We are currently in the assessment phase of the program which will supply 50 latest generation Apache helicopters to the UK. This phase includes establishing best value-for-money  for the taxpayer and will conclude in spring 2016, with a decision on procurement then following.

"We have sought proposals from both AgustaWestland and the US government, which has notified Congress. No decisions will be made until next year."

Could you amend par 4 which starts 'A decision on how' saying the assessment phase on the program ends in Spring 2016 and a decision on how the MoD intends to procure the helicopter is expected in the Summer of next year.

The Rolls-Royce RTM322 engines, which along with other locally developed systems helped to make the British version of the Apache such a success in operations in Afghanistan and elsewhere, will be replaced.

AgustaWestland's Yeovil plant in southwest England was involved in the assembly of the WAH-64D and the company has been lobbying hard for a role in the new program to help retain design and manufacturing skills at the site.

Industry sources said Boeing and AgustaWestland have been holding discussions to try and hammer out a compromise agreement that would involve the British facility in the work .

Boeing declined to comment. AgustaWestland  could not be reached for a comment

As with all DSCA notices, the sale still has to be approved by Congress and an actual contract worked out by all parties involved.

Twitter: @Aaronmehta