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Republic XF-103 (Thunderwarrior)

Supersonic Mixed-Propulsion Interceptor Proposal [ 1956 ]

The XF-103 was a Republic response to the Soviet heavy bomber threat of the early Cold War years - a missile-armed, supersonic turbojet-and-ramjet-powered interceptor.

Authored By: Staff Writer | Last Edited: 12/28/2016 | Content ©www.MilitaryFactory.com | The following text is exclusive to this site.

Before ground-based missiles provided the basis for viable air defense systems, the "interceptor" combat aircraft was the primary counter to high-flying, long-range heavy bombers. During the 1950s, amidst the growing threat (and inherent nuclear-delivery capabilities) of Soviet jet-powered bombers, the United States Air Force (USAF) sought various solutions to the problem at hand resulting in a bewildering array of conceptual, developmental, and production aircraft to suit the role.

One development of the mid-1950s became the Republic XF-103 "Thunderwarrior" (Company Model "AP-57") which sought to fulfill a USAF requirement begun in 1949 for a supersonic, technologically-advanced, missile-armed interceptor. The nature of this requirement dictated a most aerodynamically-refined shape with swept-back wing surfaces and a powerful propulsion system beyond what was conventional for fighters of the period. The USAF program sought to combine such an air vehicle with a new Fire Control System (FCS) - the Hughes "MA-1" - and new air-to-air missile technology. The initaitve was dubbed the "1954 Interceptor" and recognized formally as "Weapon System WS-201A".

From six competing proposals came three selected submissions in 1951 in the Convair XF-102 (based on its dimensionally smaller XF-92), the Lockheed XF-104, and the Republic XF-103.The Republic entry was a sleek offering showcasing a slim, slab-sided fuselage with pointed nosecone. Smallish triangular wing mainplanes were affixed at shoulder level near midships and the trailing horizontal tailplanes were mid-mounted along the fuselage's aft sides. A single vertical fin capped the empennage and all wing surfaces were highly swept along their leading edges. The cockpit, a retractable capsule, was held at the front of the design overlooking the nose in the usual way - the capsule held the ability to be raised for ground-running and collapsed for supersonic flight. All of the weaponry would be held internally to preserve the aerodynamic qualities of the interceptor. A tricycle undercarriage would be in play consisting of a single-wheeled nose leg mounted well-aft of the cockpit floor and a pair of single-wheeled main legs installed at the fuselage between the wing mainplanes and horizontal planes. The technology aboard the aircraft allowed just one crewman to be used. The FCS held the ability to take the aircraft to the target area, track the target, and engage the target on its own. Standard armament centered on 6 x Hughes GAR-3 "Falcon" Air-to-Air Missiles (AAMs) with a battery of 36 x Folding Fin Aerial Rockets (FFARs) also carried. Alternatively the interceptor could field 4 x Hughes Falcon missiles and 2 x Nuclear-tipped AAMs.©MilitaryFactory.com
One of the more in interesting design qualities of an already advanced aircraft became the mixed powerplant. Primary cruising thrust would be from a standard turbojet engine - the developmental Wright XJ67-W-1 - seated in tandem with another developmental offering, the Wright XRJ55-E-1 ramjet. The ramjet added supplementary power to the turbojet installation but required a minimum operating speed before it could be engaged effectively. It was estimated that the streamlined aircraft could reach speeds of Mach 3, operate at 60,000 feet altitudes, and sport a rate-of-climb of 19,000 feet-per-minute.

A shared intake vent at the belly of the aircraft fed air into the engines. The ductwork was such that it could be rerouted to feed the ramjet or turbojet and any given time. The ramjet provided much higher thrust and thusly greater operating speeds for the proposed interceptor. However, ramjet engines of the period were notoriously fuel-thirsty and only delivered efficiency beyond Mach 1 speeds.

Republic readied a mockup which was reviewed during March of 1953 and, from this, came a contract for three total prototypes in June of 1954. Because of the inherent nature of high-speed flight, in which high temperatures developed despite the cold environment, titanium would figure largely into the aircraft's construction. As titanium was never a material to prove easy to work with, this complicated the already-complex aircraft. The engines themselves faced mounting delays and the project's budget ballooned beyond comfortable levels. The 1954 Interceptor program was effectively cancelled in 1957 and the XF-103 fell to the pages of Cold War history. Meanwhile, the competing Convair XF-102 went on to have a healthy career as an interceptor along different lines - becoming the F-102 "Delta Dagger" (detailed elsewhere on this site). Similarly, the Lockheed submission went on to become the Mach 2-capable F-102 "Starfighter" and had a notable service career all its own.

The aforementioned mockup was all that was completed of the XF-103.©MilitaryFactory.com
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Republic Aviation Corporation - USA
United States
Operators National flag of the United States
Service Year
United States
National Origin

Ability to intercept inbound aerial threats by way of high-performance, typically speed and rate-of-climb.
Aircraft developed for the role of prototyping, technology demonstration, or research / data collection.

77.1 ft
(23.50 meters)
34.4 ft
(10.50 meters)
16.7 ft
(5.10 meters)
24,956 lb
(11,320 kilograms)
Empty Weight
42,869 lb
(19,445 kilograms)
Maximum Take-Off Weight
+17,913 lb
(+8,125 kg)
Weight Difference

1 x Wright XJ67-W-3 turbojet engine developing 15,000lb of thrust; 1 x Wright XRJ55-W-1 ramjet engine developing 18,800lb of thrust.
2,600 mph
(4,185 kph | 2,260 knots)
Max Speed
80,052 ft
(24,400 m | 15 miles)
1,553 miles
(2,500 km | 1,350 nm)
19,000 ft/min
(5,791 m/min)

MACH Regime (Sonic)
RANGES (MPH) Subsonic: <614mph | Transonic: 614-921 | Supersonic: 921-3836 | Hypersonic: 3836-7673 | Hi-Hypersonic: 7673-19180 | Reentry: >19030

36 x 2.75" (70mm) Folding-Fin Aerial Rockets (FFARs) held in an internal weapons bay.
6 x Hughes GAR-1/-3 AIM-4 "Falcon" AAMs held in an internal weapons bay.

4 x Hughes GAR-1/-3 AIM-4 "Falcon" AAMs held in an internal weapons bay.
2 x Nuclear-tipped AAMs held in an internal weapons bay.


XF-103 "Thunderwarrior" - Base Project Designation

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Image of the Republic XF-103 (Thunderwarrior)
Image from the Public Domain.
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Image of the Republic XF-103 (Thunderwarrior)
Image from the Public Domain.
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Image of the Republic XF-103 (Thunderwarrior)
Image from the Public Domain; a full-size mockup of the XF-103 is pictured.

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