US Tri-Service Designation System

MDS (Mission - Design - Series)

Utility (Standard Designations)

• Cessna U-26: One Model 206 seized by US DEA and transferred to US Customs Service. Additionally, the US Army acquired two T206H Turbo Stationair in 2021 for use at West Point. These aircraft do not appear to have an MDS designation, but have been assigned the military serials 21-01903 & 21-01970.

• Cessna U-27: Several Model 208 Caravan use by the US Army.

• Pilatus U-28 Draco: PC-12 used by USAF for special operations support & ISR.

• U-29: Next available numerical designation, in standard numerical sequence. Source: Designation-Systems.net

Utility (Non-standard, Out-of-Sequence Designations)

• Schweizer RU-38 Condor Twin: Two SA.2-38A Condor special reconnaissance aircraft used by US Army, USCG and Department of Justice. Designated out of numerical sequence, possibly using the Schweizer model number.

X = Research (Standard Designations)

• Boeing / Pratt & Whitney Rocketdyne X-51 WaveRider: Unmanned hypersonic test demonstrator.

• X-52: Designation requested for Active Aeroelastic Wing technology program, but skipped to avoid confusion with B-52. Source: Designation-Systems.net

• Boeing X-53 AAW: F/A-18 Hornet with Active Aeroelastic Wing.

• Gulfstream X-54: Unbuilt supersonic research demonstrator.

• Lockheed Martin X-55 ACCA: Dornier Do 328JET with new composite fuselage.

• NASA X-57 Maxwell: Proposed experimental light aircraft based on Tecnam P2006T with new distributed electric propulsion wings. NASA recently announced that the demonstrator would not be flown.

• X-58: This designation was skipped, and the number apparently assigned out-of-sequence to the Kratos XQ-58 Valkyrie.

• Lockheed Martin X-59 QueSST: Low-Boom supersonic flight demonstrator.

• Generation Orbit Launch Services X-60: Experimental air-launched single-stage suborbital rocket vehicle.

• Dynetics X-61 Gremlins: Experimental air-launched and air-recovered small UAV.

• Lockheed Martin X-62 Skyborg: Re-designation of NF-16D VISTA test aircraft.

• X-63: Designation appears to have been skipped when X-65 was assigned to the CRANE project.

• X-64: Designation appears to have been skipped when X-65 was assigned to the CRANE project.

• Aurora Flight Sciences X-65 CRANE: DARPA Control of Revolutionary Aircraft with Novel Effectors project.

• Boeing X-66: NASA Sustainable Flight Demonstrator program with Transonic Truss-Braced Wing.

• X-67: Next available numerical designation, in standard numerical sequence (unless X-63 & X-64 are still available).