The U.K. is facing a four-year gap in its carrier-borne airborne early warning (AEW) capability as the Defense Ministry searches for a successor for the long-serving Westland Sea King Mk7 fleet.

Initial work is underway to replace the fleet of radar-equipped Sea Kings, which have been providing aerial surveillance for Royal Navy carriers and battle groups since the early 1980s. The program, called Crowsnest, is charged with finding the replacement for this capability and a range of options is being studied.

According to questions asked in Parliament on Nov. 19, Crowsnest will enter its assessment phase in 2013 and has “not yet passed its main investment decision point,” says Philip Dunne, minister for defense equipment, support and technology. The project became part of the Defense Ministry's core equipment program under the Planning Round 12, announced in May.

Throughout the post-war years, the Royal Navy had an organic AEW capability for its conventional aircraft carriers, but when these were retired in the late 1970s, replaced by the Invincible-class anti-submarine warfare ships—essentially light carriers designed to carry ASW helicopters and BAE Systems Sea Harrier fighters for air defense—commanders believed there was no longer a need for AEW capability.

But the 1982 Falklands conflict, which saw several U.K. ships sunk or damaged due to Argentine air and missile attacks, led to the creation of a helicopter-borne AEW capability, which has rapidly evolved. Today, the Royal Navy has 13 Sea King Mk7 helicopters equipped with the Thales Searchwater radar system. In recent years, the rotorcraft has also undertaken the overland surveillance mission in Afghanistan, supporting U.S. Marine Corps operations in rural areas of Helmand Province, using the radar's ground moving target indicator mode.

The Searchwater radar is mounted on the Sea King in a distinctive radome protected by a Kevlar bag, which inflates and then lowers underneath the aircraft inflight. But these Sea Kings, along with those used for search-and-rescue and amphibious assault mission, will be eliminated from the U.K. inventory at the end of 2016, while the first two Mk7s will be retired in 2013. Crowsnest envisages the replacement capability to be in service in 2020, in time for use on the new Queen Elizabeth-class carriers. But this leaves a four-year gap in which U.K. ships will not have AEW, although Dunne added that other systems could fill the void in the interim.

Officials working on Crowsnest have determined that any replacement system will be fitted to the AgustaWestland EH101 Merlin HM2 helicopter. The Navy Merlin fleet is currently being upgraded from HM1 to HM2 standard as part of the Merlin capability sustainment program being undertaken by AgustaWestland and Lockheed Martin. The first Merlin Mk2s are due to reenter Royal Navy service in 2013.

Under Crowsnest, all 30 of the HM2s will be fitted for the Crowsnest. Ten system sets will be purchased with eight Merlins to be fitted out at any one time. A critical part of the specification is that the role change from ASW and AEW must take 24 hr. or less.

Some options are offered. The first is the AgustaWestland/Thales concept of simply reusing the current Searchwater radars and mounting them from the rear of the Merlin with the radar mounted on a hinge that drops down below the aircraft. But Royal Navy Merlins are not fitted with a rear ramp, so Thales and AgustaWestland are studying an option that would see the radar lowered into the airflow on the rotorcraft's port side on two rails. Navy officials are concerned that the method may not meet the 24-hr. role-change requirement. However, they like that the system, because it is already owned by the Defense Ministry, is relatively low-cost. Also, it can be transplanted from one platform into the other.

The alternative is Lockheed Martin's Vigilance system. This uses a pair of Northrop Grumman AN/APG-81 active, electronically scanned array radars from the F-35 Lightning II, fitted in pods, one on each side of the aircraft. Each array is capable of providing 120 deg. of coverage. To achieve the full 180 deg., the radar will be mounted on a 30-deg. pintle.

Lockheed Martin say a production pod would weigh roughly the same as an air-launched torpedo and could be installed and removed from the aircraft in less than 2 hr. The company also asserts the system would be “plug and play” given its involvement in the development of the Merlin Mk2's mission system. A Merlin fitted with a prototype Vigilance pod is due to fly in the U.K. imminently.

Although not offered for Crowsnest, the team also studied and eliminated the configuration of the Italian navy's AEW mission-configured EH101s, which have a Selex Galileo Heliborne Early Warning 748 surveillance radar fitted in an enlarged radome under the forward fuselage.

Royal Navy commanders will also have to decide what to do with the experienced tactical mission commander and tactical aircraft control officers, who will have no platform to fly on after 2016.

Consideration is being given to sending personnel to the U.S. to join Navy E-2 Hawkeye units, similar to Project Seedcorn, in which people from the BAE Systems Nimrod maritime patrol aircraft community flew with other air forces to maintain their MPA operations skills following the cancellation of the Nimrod MRA4 program in 2010.