An audacious project to convert land-based helicopters for shipborne amphibious operations has been given the go-ahead by the U.K. Defense Ministry.

The £330 million ($546 million) program, awarded to AgustaWestland in December but only formally announced on Jan. 29, helps to secure the U.K.'s amphibious power projection capabilities, which will become a key part of the country's ability to mount a Responsive Force Task Group (RFTG) on its future Queen Elizabeth-class aircraft carriers.

The Merlin Life Sustainment Program and ship optimization is unusual in that it will hand over 25 of the Royal Air Force's 28 land-based EH101 Merlin Mk. 3 and Mk. 3A helicopters—none of which has ever landed on a ship—to the Royal Navy's Commando Helicopter Force (CHF) and convert them into fully marinized assault helicopters ready for use from aircraft carriers.

The program is unique in the annals of rotary-wing aviation. Normally, aircraft are purpose-built for naval operations and end up becoming land-based later in their careers.

The plan is part of a long-term effort to streamline the number of frontline helicopter types in service with the U.K.'s Joint Helicopter Command (JHC) to four: the Boeing CH-47 Chinook, EH101 Merlin, Apache attack helicopter and AW159 Wildcat reconnaissance and scout helicopter.

The Westland Sea Kings, known as Junglies, currently used by the CHF will be retired at the end of March 2016 as part of a wider retirement program of that type.

The process of handing over the helicopters to the Royal Navy has already begun; navy crews have been flying the aircraft since 2012 at the main operating base of RAF Benson, England. More navy personnel have been arriving at the station, and the navy will take command of the fleet when manpower levels reach 50%, which is expected in September.

AgustaWestland will use its experience from the development of a naval transport version of the EH101—now the AW101—for the Italian navy. The company will remove the current tail-rotor system and replace it and the main rotor masts with a folding version. The aircraft also will be given strengthened landing gear, deck lashing mounting points and a new fast-roping point.

The helicopters will be upgraded with the avionics suite used in the update of the Royal Navy's current fleet of Merlin helicopters used for antisubmarine and antisurface warfare. Navy officials hope this will allow pilots to be cross-trained on both variants, helping to cut training costs.

Because the program is also converting six former Danish air force helicopters purchased by the U.K. in 2008—known as Merlin Mk. 3As—AgustaWestland also must develop a common emergency egress system for use on both versions, which have different configurations. The upgrade will ready the rotorcraft for frontline operations for the first time. In Royal Air Force service, they supported training operations only.

“For contingency operations, we are expected to operate in multiple environments,” said Cmdr. Steve Doubleday, chief of staff for the CHF at the International Military Helicopter conference here on Jan. 24. “The aircraft is proven on land, but any capability development also has to be able to work in hot and high and dusty environments.”

The program will include some obsolescence updates to improve maintainability and reliability, as well. Without the program, the planned out-of-service date for Merlins would have been 2017.

The first two helicopters will begin the conversion process at the end of this year, with the first fully converted Mk. 4s expected to be available for trials in September 2017. An initial operating capability with the Merlin Mk. 4 with seven helicopters is expected in early 2018 and full operational capability in 2020.

In order to avoid a Royal Navy amphibious transport capability gap between the retirement of the Sea King and the introduction of the first Mk. 4 models, seven Merlins will be given a folding main rotor head, additional communications equipment and modified landing gear to support shipborne operations, should a deployment arise. These will be known as the Merlin Mk. 3i, for “interim.” Those seven later will be converted to the full Mk. 4/4A standard.

The £330 million covers AgustaWestland's contract; another £124 million allocated to the program will be spent on supporting training, tests and infrastructure associated with the program.