RAT55: What is this USAF Boeing 737-based aircraft and why is it so secretive?
August 24, 2025
Normally hidden away from view in a remote hangar at an airfield deep within Area 51 in the Nevada Desert, one of the US Air Force’s most secretive (and unseen) aircraft has made a rare appearance.
Spotted by eagle-eyed aviation photographer Michael Rokita from a mountain located 26 miles (42 km) from the top secret base, the specially modified Boeing NT-43A (a military variant of the Boeing 737 passenger jet), which goes by the moniker ‘RAT55’, was viewed performing a flight over the surrounding area.
Avionul secret RAT55, surprins în manevre de tip touch-and-go la baza militară, este legat de Hangarul 18, alimentând speculațiile despre tehnologii misterioase și teste cu bombardierele invizibile, precum B-2 Spirit. pic.twitter.com/bM0JCXWBdL
— unumihai (@unumihaii) August 22, 2025
As shared by The Aviationist, RAT55 was seen carrying out circuit practice at the US Government’s classified Groom Lake facility, performing a series of touch-and-goes before ending with a full-stop landing.
The flight was remarkable for two reasons: firstly, it confirmed that the aircraft is still airworthy, and secondly, that it is based at Groom Lake, a point that had been unconfirmed until now. Specifically, the aircraft was seen returning to Hangar 18, suggesting this is its permanent home.
What is the Boeing NT-43A known as ‘RAT55’?
RAT55 is the name given to a version of the USAF’s NT-43A military twinjet, a specific aircraft with tail number 73-1155.
Flying as a specially modified military variant of the Boeing 737-200, the name RAT55 is thought to derive from the aircraft’s primary role as a radar airborne testbed (RAT) with the ‘55’ being taken from the last two digits of the plane’s tail number.
The aircraft is believed to use the callsign “RAT55” (or even “RATT55”) over the radio whilst operating into and out of Groom Lake.
RAT55 has spent much of its military career crisscrossing the airways over the remotest parts of Area 51, which spans the deserts of South-Central California and Southern Nevada. It has also been seen flying near the top-secret Edwards Air Force Base in California.
The aircraft’s presence and movement are kept highly secret as the plane fulfils a vital role unlike any other aircraft in the US military performs. It is thought that RAT55 is used for the development of radar-evading technology, often referred to as stealth technology.
What does RAT55 do?
RAT55 collects data using two huge radar arrays located on the forward and rear of the fuselage to take highly accurate measurements of the radar signatures of the USAF’s stealth aircraft while flying near to, or alongside, them.
Using these readings and providing the collected data to military scientists, the data can be used to develop new aircraft skin technologies that can be developed to minimise radar conspicuity for military aircraft.
While certain ground stations can collect certain data of this type, the additional information collected by an airborne platform, such as RAT55, is highly accurate and therefore valuable to the designers working on the most top-secret military aircraft designs of tomorrow.
It is believed that RAT55 is adaptable in this role, with the aircraft having been spotted in the past with a vast array of additional mounted equipment, extrusions, dorsal fins, and other aerials and sensors all fitted to perform tasks that are generally shrouded in secrecy.
With the USAF pressing ahead with the development of two new manned stealth military aircraft programmes – the Northrop Grumman B-21 Raider and the Boeing F-47 – there is still demand for RAT55’s specialist capabilities. The aircraft may also be used on other aircraft programmes currently under development, the details of which the public may never know.
RAT55 has been viewed most often by the general public when escorting B-2 Spirit stealth bombers on post-maintenance flights. Such sorties are performed to verify that the stealth characteristics of the B-2s have been maintained through the maintenance process and that they can be cleared to return to active service.
RAT55 working with a B2 #rat55 #b2 #ratt55 pic.twitter.com/mezwJKtJd8
— Julian Elnasser (@LAXSPOTTER97) May 28, 2025
More about Hangar 18 and Area 51
Seen performing its latest flight on August 13, 2025, RAT55 was spotted being returned to Hangar 18 at Groom Lake following its brief outing.
Hangar 18 is notorious among military historians and conspiracy theorists alike as it is thought to be the location in the US Government carries out its most secret projects, including its highly classified new aircraft projects.
Additionally, Hangar 18 has long been rumoured to be where the US Government stores evidence of Unidentified Flying Objects (UFOs) and extra-terrestrial/alien activity, which adds an air of mystery and an elevated level of secrecy to the location itself.
— Jason (@JasonZicker) May 22, 2025
Even RAT55 tends to alter its radio callsign from time to time while operating in the vicinity of Area 51 – TWZ noted it flew in May under the callsign STRMY29. It often turns off its transponder, making its precise movements impossible to track by anyone who doesn’t need to know of its presence, all of which adds to the intrigue.
Historically, the US government denied the existence of Area 51 until 2013, when the US Government formally acknowledged its presence, stating it was used solely for the testing and development of future USAF military aircraft.
Nearing the end?
Although the RAT55 is bristling with highly advanced technology and cutting-edge hardware, the airframe on which it is mounted is not of the modern era. The first Boeing 737-200 flew in 1967, and Planespotters data suggests RAT55 was delivered in July 1974, making it over 51 years old.
Nevertheless, RAT55 clearly flies on and is yet to be replaced in its vital yet highly secretive role.
