US Tri-Service Designation System

MDS (Mission - Design - Series)

O = Observation (Standard Designations)

• de Havilland Canada RO-6: Several DHC-8-315 acquired by the US Army for the Airborne Reconnaissance Low program.

• O-7: Next available numerical designation, in standard numerical sequence. Source: Designation-Systems.net

P = Patrol (Standard Designations)

• Boeing P-8 Poseidon Patrol aircraft based on Boeing 737, replacing the USN P-3 Orion.

• Sierra Nevada P-9: Several Bombardier Dash 8 types used by the USAF for surveillance. Source: Aviation Week

• P-10: Next available numerical designation, in standard numerical sequence. Source: Designation-Systems.net

R = Reconnaissance (Standard Designations)

• Lockheed TR-1: The only aircraft designation assigned in this sequence, and even then it is non-standard with the "T" representing "Tactical" instead of the Modified Mission "Training". Surviving TR-1 aircraft were redesignated U-2R.

• R-2: Next available numerical designation, in standard numerical sequence. Source: Designation-Systems.net

S = Anti-Submarine Warfare (Standard Designations)

• Lockheed S-3 Viking: US Navy carrier-based ASW aircraft. Retired in 2016 with no direct replacement.

• S-4: Next available numerical designation, in standard numerical sequence. Source: Designation-Systems.net

T = Trainer (Numerical Shenanigans)

• Fairchild T-46 Eaglet: Two prototypes for the cancelled USAF NGT program to replace the T-37 Tweet.

• Beech T-1 Jayhawk: The Trainer numerical sequence was restarted for this USAF airlift & tanker trainer. At the same time, the T-48 and T-49 designations were reserved for the planned USAF and USN versions of the JPATS airframe. Source: Designation-Systems.net

• T-2: This designation in the restarted numerical sequence appears to have been skipped, likely due to the North American T-2 Buckeye still being in service.

• Slingsby T-3 Firefly Designation assigned to T67M260 acquired by the USAF.

• T-4: This designation was skipped so that the JPATS could be assigned the T-6 designation. Source: Designation-Systems.net

• T-5: This designation was skipped so that the JPATS could be assigned the T-6 designation. Source: Designation-Systems.net

• Beech Raytheon T-6 Texan II Designation of the winning JPATS contender, used by the US Air Force and US Navy.

• Cessna T-47A The numerical sequence jumped back to this previously skipped designation for several Citation II acquired by the US Navy as navigation and radar trainers.

• Cessna OT-47B Tracker Designation confusingly assigned to a different Cessna, the Citation 560, despite there already being a suitable designation for a similar Cessna, the UC-35.

• T-48: Originally reserved for the USAF version of JPATS (see T-1 above), this designation was reserved for the USN MPATS program to replace the T-39. This program seems to have been deferred indefinitely.

• Boeing CT-49 Two ex-Luftwaffe C-137 and one ex-airliner Model 707-329C used for the NATO AEW&C Trainer Cargo Aircraft program. It is unclear why these aircraft would be assigned US designations.

• T-50: Designation reserved for the Lockheed/TAI T-50 Golden Eagle, even though the US does not use this aircraft. Apparently this was done to avoid any potential confusion. Source: Designation-Systems.net

• Cessna T-51: Designation for three Model 150 used by the US Air Force Academy.

• Diamond T-52: 20 DA40 Diamond Star acquired for use at the US Air Force Academy.

• Cirrus T-53 Kaydet II: 25 SR20 acquired to replace the T-52 used at the US Air Force Academy.

• Boeing-Saab T-7 Red Hawk Just when it seemed like the Trainer sequence was back in order, this designation was assigned to the winner of the T-X program to replace the T-38 Talon.

• Beech T-54: Shaking up the numerical sequence again, this designation has been assigned to 10 King Air 260 ordered by the US Navy to replace the T-44 Pegasus multi-engine trainer. First deliveries are planned for early 2024.

• T-8 and/or T-55: One or both of these seem to be the next available standard designation for the Trainer sequence. Potential programs include the US Navy Undergraduate Jet Training System (to replace the T-45 Goshawk), the USAF Advanced Tactical Trainer, and the US Navy Tactical Surrogate Aircraft.