If you happened to be at Birmingham Airport on the afternoon of 15 July, you would have seen something that looked like a mistake: a Boeing 737 with a large rectangular fin bolted to its spine, painted an unlovely metallic green, climbing out over the West Midlands.

It was not a mistake. It was WT002, the second of the Royal Air Force's three E-7 Wedgetails, making its first flight since being torn apart and rebuilt as an airborne early warning aircraft. It stayed up for about two hours. Boeing confirmed the flight the following day.

The green is the interesting part, and it is worth explaining, because almost every new aircraft you have ever seen photographed has been through this stage and almost nobody photographs it.

Why it is green

The coating is primer. Aluminium aircraft structures corrode, and they start corroding the moment they are exposed, so a converted airframe gets sealed in a protective layer as soon as the metalwork is finished. The green tint comes from the chromate compounds traditionally used in aerospace primers. It is temporary, it is functional, and it also serves as the base coat for the finished paint scheme.

What is unusual is flying in it. Most aircraft are painted before they fly because paint is applied on the ground and grounded aircraft cost money. But on a conversion programme the sequence runs differently: prove the aeroplane works, then spend three weeks and several hundred kilograms making it look like an air force owns it. WT002 will go for paint before entering the test and evaluation phase.

The gap this is closing

Britain retired its E-3D Sentry fleet in 2021 and has been without a sovereign airborne early warning aircraft ever since. Five years is a long time for a nuclear-armed NATO member with global commitments to have no way of seeing beyond the horizon on its own.

The first aircraft, WT001, arrived at RAF Lossiemouth on 21 May after systems activation and radar calibration work at Boscombe Down. It is in the final stages of ground and flight testing before formal handover from Boeing to the RAF. The third and last airframe is still in conversion at Birmingham.

The phrase to notice there is "see the need." Service entry has been promised for 2026 and Boeing has still not named a handover date. Nobody involved is relaxed about the schedule.

Three aircraft, and the arithmetic of that

Britain signed for five Wedgetails in 2019. The 2021 Integrated Review cut that to three as a cost-saving measure, and that decision has been argued about ever since.

The arithmetic is unforgiving. With three airframes, one in deep maintenance and one in training or transit leaves you one aircraft. Sustaining a single orbit continuously over any length of time is difficult. Sustaining two is not realistic. For comparison, Australia, which originated the type, operates six.

What Britain does have is a very good aircraft. The E-7 replaces the E-3's rotating dome with a fixed Northrop Grumman MESA array in a dorsal fin, which sounds like a detail and is not. A mechanically rotating antenna can only look where it happens to be pointing. An electronically scanned array steers its beam instantly and can search, track and control fighters at the same time, in different directions, without moving a single part.

The video above is a walkthrough of an Australian E-7A, which will give you a far better sense of the interior than any photograph of the outside. The RAF aircraft is the same basic machine.

The money underneath

The flight was not the only Wedgetail news that week. Boeing Defence UK was awarded a sustainment contract worth about 127.5 million pounds to support the E-7 fleet, part of more than 240 million pounds in RAF support work that also includes a 115.2 million pound extension covering the nine P-8 Poseidons at Lossiemouth. The E-7 award is expected to support around 180 jobs in Scotland, with 60 to 80 more to be created and four apprenticeships.

Sustainment contracts are the least glamorous documents in defence and among the most revealing. You do not sign a multi-year support deal for a fleet you expect to be arguing about. Putting the maintenance workforce in place at Lossiemouth is Boeing and the Ministry of Defence both behaving as though the Wedgetail is about to become a real, flying, operational thing rather than a programme.

Which, green paint and all, it now nearly is.

Sources: ADS Advance, FlightGlobal, Aerospace Global News, Aviation Week, Royal Air Force, Army Recognition.