World's Most Secretive 737 Just Made A Very Rare Appearance

Yahoo

23-05-2025

RAT55, U.S. Air Force Materiel Command's extremely shy NT-43A/737-200 converted into a grotesquely modified radar cross-section measurement platform just flew across the country for an unknown reason. During its trip, it made two stops, one in Arkansas and one in Texas, the latter offering very rare close-up views of Earth's most fascinating 737 going about its business.
RAT55 arrived at Rick Husband International Airport in Amarillo, Texas, 'at 2:40 pm and departed at 3:40 pm. It was cleared back to Tenopah Test Range Airport,' Jason Zicker, an aviation photographer who took the videos below and posted them on social media, told TWZ. Zicker said he was alerted to RAT55's arrival by a fellow plane spotter.
pic.twitter.com/cZxgvCzIW4
— Jason (@JasonZicker) May 22, 2025
RATT55 departing KAMA https://t.co/zFyVP6F7Zw
— Jason (@JasonZicker) May 22, 2025
'As far as I know, it was just for gas,' said Zicker, who was kind enough to let us use his video. 'RAT55 did have a flight plan to come here a couple of months ago, but never showed up.'
The aircraft flew from the Nevada Test and Training Range (NTTR) to Northwest Arkansas National Airport. It stopped at Amarillo on the way back, likely for fuel. It isn't clear why it went to Arkansas at this time. We asked Air Force Materiel Command if they could provide any information as to RAT55's puzzling trip and they replied: 'Regarding your query, I do not have any details to provide.'
It is interesting to note that King Aerospace has a presence at Northwest Arkansas National Airport. In 2022, RAT55 appeared at a different King Aerospace facility at Admore Municipal Airport in Oklahoma during another rare outing. Whether or not its latest trip is again tied to a visit to this company, which specializes in heavy maintenance and deep modification work, including for the U.S. military, is unknown at this time. TWZ has reached out to King Aerospace for more information.
#A10635 as #RATT55/#STORMY29Up from Groom Lake KXTA to Northwestern Arkansas National Airport KXNA. Audio of STORMY29/RATT55 getting cleared to land at KXNA. pic.twitter.com/Hs0nXmp6Lq
— Norb (@norb420) May 20, 2025
The name RAT55 is actually used for the jet's callsign, although as RATT55, with an extra t. On this particular outing, the jet has been using the callsign Stormy 29.
Looks like their callsign today was STRMY29 and not RATT55 pic.twitter.com/DLnnqDWKeL
— Thenewarea51 (@thenewarea51) May 21, 2025
The 'RAT' in the name stands for Radar Airborne Testbed, while the '55' refers to the last two digits in its tail number. RAT55 spends most of its flying life in the vast and remote range complexes that span South-Central California and Southern Nevada. The aircraft seems to live at the high-security Tonopah Test Range Airport (TTR) — famous for its shadowy aircraft programs — and spends time in the skies near Area 51 and Edwards Air Force Base. While the one-off NT-43A has ventured beyond its usual protected operational confines — it needs major servicing just like any other 737 — usually these trips seem to be planned to expose the aircraft to minimal public eyeballs. That is clearly no longer the goal.
Regardless, RAT55 is unlike any other aircraft on the planet, and it is absolutely critical to the development and sustainment of America's aerial stealth technology. Simply put, RAT55 uses its two huge radar arrays — one front and one back — to take fine measurements of the radar signatures of stealthy aircraft while flying through the air near them. It does this to validate low-observable designs and skin treatments. It also has electro-optical/infrared capabilities above its radomes and can be fitted with dorsal fairings for other systems. While there are facilities on the ground that can take similar measurements of aircraft flying through the air, doing it from another specially-equipped aircraft in the air allows the target to be measured from every angle, including from overhead aspects, and continuously.
Even when B-2 Spirits come out of depot maintenance, they usually spend time in the sky with RAT55 to validate that the work done fits established design goals and parameters. That is the most visible of the NT-43A's work, but the aircraft is also involved with the most advanced and secretive stealth aircraft development programs in the Pentagon's portfolio, many of which we don't know about and likely never will.
Got a glimpse of #rat55 while in Death Valley this week with a #B2 bomber pic.twitter.com/O5hQnfJmft
— Marc Bierdzinski (@mbplan) October 29, 2020
Considering all of the combat aviation developments now underway in a new era of so-called 'great power competition,' RAT55 is presumably busier than ever, and will be flooded with work soon as many programs mature into a flying state. From the B-21, to a plethora of new advanced drones, to the F-47 next-generation fighter, the stealth business is booming. At the same time, RAT55 is a very old aircraft, and dwindling support for first-generation 737s is surely becoming an issue. With this in mind, it is somewhat puzzling why it isn't being replaced or at least augmented. Then again, it could be, and we won't know until that new aircraft materializes somewhere.
That's the abbreviated version of what we know about RAT55, you can read more about the aircraft and see the best images ever taken of it in this past feature of ours.
While we don't know why RAT55 came out of the shadows for this jaunt across the U.S., it sure was a great opportunity for aviation enthusiasts to spot a truly one-of-a-kind plane, and a very clandestine one at that.
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