Unmasking Northrop Grumman's XRQ-72A

However, AFRL only requested a formal designation for the Great Horned Owl drone in January 2017, according to the documents we received via the FOIA request. "It is planned that the GHO [Great Horned Owl] demonstrator would complete a series of flights at the Acoustic Research Complex operated by AFRL/RH [Airman Systems Directorate] on the White Sands Missile Range incorporating the hybrid power and propulsion system, and then be available for future demonstrations of additional technology and/or vehicle configurations," the memorandum explained. 

What's also interesting is that AFRL asked for an X-plane designation, which are typically applied only to purely experimental aircraft. One notable exception was the Bell X-16, which was publicly described as a high-altitude testbed, but was, in fact, a competitor to the famous U-2 Dragon Lady spy plane.

"The X-## Mission Design Series Assignment is very important at this time to highlight to the aerospace R&D community the importance of the development of hybrid power and propulsion for future USAF aircraft," the memo noted. "While potential benefits to a broad range of future vehicles have been identified, such a dramatic change in the design paradigm is a slow process. The X-## designation for the GHO will dramatically improve awareness of the research and help preserve the technical achievements, increasing opportunity for technical transition of the experimental results and design philosophy to future USAF air vehicles."

It's not clear how the final XRQ-72A designation, which the Air Force approved in March 2017, came about. The "XRQ" prefix is very much not an X-plane designation and is more fitting for a prototype of a potentially operational platform. There numerous examples of experimental drones with "XQ" or just "X" prefixes, such as the Kratos XQ-58A Valkyrie and the Lockheed Martin X-44A, as well as the still curious YQ-11 prototype designation for the General Atomics Predator C/Avenger, so this appears to have been a deliberate decision. 

The number 72 is also wildly out of sequence for either the X-plane category or the drone category in the U.S. military's joint-service aircraft designation system. It is a number that has been informally applied on multiple occasions to advanced intelligence, surveillance, and reconnaissance aircraft designs in the past, as a reference to being a spiritual successor to the iconic SR-71 Blackbird spy plane.

In 2018, IARPA also initiated a follow-on project called Little Horned Owl, which had similar goals to Great Horned Owl, but called for a notably smaller overall design that would only have to carry a 10-pound payload. There was also a requirement for "innovative battery architecture to improve flight times for battery-only flight" and "runway independent operation (minimal ground support equipment)."

Regardless, as IARPA noted in 2011, there is a clear demand for the kind of technologies developed under the Great Horned Owl program. A drone with relatively long endurance and very quiet operation would enable persistent surveillance of targets of interest with a reduced likelihood of detection. 

This, of course, would hardly be the first time the U.S. Intelligence Community, or the U.S. military, has acquired or otherwise experimented with ultra-quiet aircraft for reconnaissance and covert operations. The CIA famously used a pair of Hughes 500P helicopters, also known as the "Quiet Ones," to conduct a top-secret wire-tapping operation in North Vietnam during the Vietnam War. The U.S. Navy and the U.S. Army also experimented with very-quiet manned surveillance aircraft, such as the YO-3A Quiet Star, during the Vietnam War. 

During the 1980s and 1990s, the Army, as well as the U.S. Air Force and the CIA, further pursued higher-flying manned surveillance aircraft with low acoustic signatures, most notably the RG-8A Condor powered glider, some of which later found their way into U.S. Coast Guard service. The Coast Guard went on to fly the unique RU-38A Twin Condor, as well. You can read more about these aircraft, and the Coast Guard's attempts to develop a successor, in this past War Zone piece. 

When it comes to more modern quiet drones, The Defense Advanced Research Projects Agency (DARPA) has been pursuing similar developments for U.S. military use. In 2006, Lockheed Martin also supplied a hand-launched, electrically-powered drone called Stalker to an unnamed customer, reportedly U.S. Special Operations Command, specifically to meet a requirement for a quieter unmanned aircraft that opponents would have a harder time detecting. More recently, the company developed a propeller-driven flying wing design, called Fury, which is visually similar to the RQ-170, albeit smaller, and that also has a reduced acoustic signature.

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