Republic F-105 Thunderchief

The F-105 Thunderchief was a Cold War product of the Republic Aviation Corporation and became the company's last production aircraft before its merger with Fairchild. The platform was developed as a successor to the F-84 series (also a Republic product) and carried on the former's nuclear munitions capability. The F-105 featured an impressive internal weapons bay along with external hardpoints and played a pivotal role in the Vietnam War, operating as both strike fighter and air defense suppression platform ("Wild Weasel").

Development
Origins of the Thunderchief series lay in a 1951 Republic private venture initiative to replace existing Republic F-84F Thunderstreak/Thunderjet aircraft in the high-performance, supersonic tactical fighter-bomber role. In fact, design of the Thunderchief was already under way before the F-84 was even in service with the United States Air Force. Thunderchief The design was brought to the USAF and quickly made an impression thanks to its multi-role capabilities coupled with impressive performance potential. The prototype YF-105A was made ready and saw her first flight on October 22nd, 1955, featuring a massive airframe wrapped around an equally powerful Pratt & Whitney J57-P-25 turbojet engine of 15,000lb thrust. Only two of these prototypes were eventually built but quickly became the largest single-seat, single-engine combat aircraft in aviation history . These prototypes were followed by four YF-105B models fitted with newer J75-P-3 engines of 16,470lb thrust and forward-swept engine inlets at the wing roots.

Production models were received several years later, these in the form of F-105B models and based on the YF-105B prototypes, arriving in the USAF inventory on May 27th, 1958. F-105B's were produced in 75 examples and were made up of a batch consisting of 10 pre-production and 65 production aircraft. The USAF was interested in photo-reconnaissance variants of the F-105B design with the intended designation of RF-105B, but decided to go with the RF-101 Voodoo variants due to their already proven status. Despite this, at least three RF-105's had already been completed (these with flat camera noses and no photographic equipment) but these were just re-designated as JF-105B's. At the time of its inception, the Thunderchief became the USAF's heaviest and most technologically complex system ever fielded by the branch. B-models also served with the USAF "Thunderbirds" performance group for a time, but they were later dropped in favor of the former Thunderbird mount - the F-100D Super Sabre - after a B-series Thunderchief broke up in flight. A two-seat trainer was planned as the F-105C but was cancelled before any production had begun.

The F-105D represented the "definitive" production Thunderchief, numbering some 610 total examples, delivered first to USAF forces based in Europe. These were based on the single-seat F-105B models and marketed as improved versions with all-weather strike fighter capability and a beefed up navigation/attack suite. D-models appeared in 1959, four years after the prototype YF-105A's first successful flight. F-105D models represented nearly 75% of all Thunderchief production, numbering some 610 total units in production. Marked improvements in the type included an increase to the overall ordnance load (12,000lbs up from 8,000lbs) with 8,000lbs alone fitting into the internal bomb bay and the remaining 4,000 on four underwing pylons (two to a wing). Power was derived from a single Pratt & Whitney J75-P-19W engine of 24,500lbs of thrust. Performance specs included a 1,390 mile per hour top speed with a 778 mile per hour cruising speed, a range of 2,206 miles and a ceiling of 51,000 feet.

Externally, F-105D's were similar to the preceding F-105B's with the exception of the longer and wider radome housing the NASARR radar. The powerful radar system allowed the F-105D to attack enemy targets "blind" if need be whereas B-models featured a simple radar ranging cannon sight in the nose. D-models were also differentiated by the use of a nose cone-mounted pitot tube as opposed to the mounting on the wingtip as in the B-models. Additionally, F-105D's were fitted with an arrestor hook at the base of the empennage. This was utilized to prevent the aircraft from overshooting the runaway on landing. Despite this "navy" like quality, the Thunderchief was never intended nor was it designed to be operated from carriers. Thunderchiefs D-models are oft-noted for their extensive combat service in the Vietnam War and were ultimately retired from USAF service by 1980, replaced by the more capable McDonnell F-4 Phantom II's, effectively cutting the planned production total of the Thunderchief by 50%. The follow-up F-105E model would have been a two-seat model based on the D-models. These were inevitably cancelled with no production examples to show for it.

The F-105F became a two-seat dual-role trainer/fighter-bomber and saw first flight in 1963. These were produced in 143 total examples, the second highest production total of all Thunderchief models. A second cockpit was added to the fuselage design with the two pilots seated in tandem. F-models were fitted with a single Pratt & Whitney J75-P-19W engine of 24,500lbs of static thrust with afterburner and 26,400lbs of static thrust with water injection. Ordnance limitation was a reported 14,000lbs of conventional munitions and specialty weapons. The standard close-in M61 20mm cannon was retained. Fifty-five of these models were later converted to the "Wild Weasel" role - charged with destruction of enemy surface-to-air missile sites - and became series designation EF-105F models. Production of all F-models ran from 1963 through 1964.

Modifications and improvements of these EF-105F systems eventually produced the F-105G Wild Weasels. F-105G's were powered by a single Pratt & Whitney J75-P-19W of 26,500lbs of thrust. Performance specs included a top speed of 1,386 miles per hour, a cruising speed of 596 miles per hour, a range of 1,500 miles and a ceiling of 50,000 feet. Armament appropriately consisted of anti-radiation air-to-surface missiles and specialized radar detection equipment.

Design
The F-105 Thunderchief sported sharp, clean lines throughout - from the pointed nose to the engine exhaust extending out beyond the vertical tail fin. The single-seat cockpit was positioned towards the forward portion of the fuselage and seated in an integrated design placement which flowed with the smooth contours of the aircrafts unique design. Mid-wing monoplane wings were swept back and partnered with smaller tail planes to either side of the rear fuselage. The undercarriage was of a tricycle design with two main landing gears recessing into each wing and a nose wheel recessing into a position under the cockpit seating area. Engine intakes were positioned at the wing roots to either side and to the rear of the pilots position and fed a single Pratt & Whitney J57-P-5 engine of 23,500lb thrust with afterburner. The intakes also deserve special mention with their unique implementation - forward-swept on the outboard sides and recessing inward toward the fuselage sides. From a top-down or ground-up perspective, this added to the Thunderchiefs already definitive appearance. When on the ground, Thunderchiefs took on a notoriously high position - with the nose portion distinctly elevated - requiring a step ladder nearly twice the height of an average pilot. Armament would be held on external hardpoints with an optional internal bomb bay load - in any case, the system was fully nuclear-capable.

Armament
Standard armament for the Thunderchief was a single M61 Vulcan 20mm cannon, firing at an impressive 6,000 rounds per minute. This short-ranged armament was supplemented with a mix of externally- or internally-held ordnance in the form of conventional drop bombs of 750- and 1,000-lbs, fire bombs, air-to-air missiles, air-to-surface missiles, 2.75" rocket pods and other specialty (nuclear or otherwise) weapons as needed, carried either externally or internally in a bomb bay under the fuselage. In total, Thunderchiefs could be outfitted with up to 8,000lbs of munitions to tackle a variety of roles with this total often compared to that of an entire formation of World War 2 bomber aircraft - such was the capability of the system from the start. 450-gallon fuel tanks were also part of the ordnance array, as was a "buddy" refueling tank. Additional systems included external chaff and flare dispensers.

Operational Service
The definitive F-105D models served extensively in the Vietnam War, fielded by the United States Air Force following the Gulf of Tonkin incident. In all, the type flew 75% of all aerial sorties against North Vietnamese targets in a four year span, taking part in the impressive and massive air campaign known as "Rolling Thunder". The aircraft proved its effectiveness, reliability and value against a variety of targets in a variety of designated roles, showcasing its impressive munitions-carrying and performance capabilities. Despite their nuclear-capable origins, the Thunderchief was fielded exclusively with conventional ordnance and was not limited to ground kills - several Thunderchiefs gained multiple air-to-air kills of enemy MiG fighters during the conflict. Operators of the aircraft included the 357th Tactical Fighter Squadron of the 355th Tactical Fighter Wing operating out of Thailand and the 388th Tactical Fighter Wing (the latter as Wild Weasels). With their heavy involvement in the air war (surpassing some 20,000 combat sorties), Thunderchiefs inevitably paid an awful price - with many (at least 350) being downed over Vietnam, many by North Vietnamese anti-aircraft fire. Thunderchiefs were gradually phased out with the arrival of the classic McDonnell F-4 Phantom II.

Conclusion
Despite its sheer size, complexity and high production cost, the Thunderchief became a top-notch performer in the Vietnam Conflict. It's multi-faceted design allowed for the system to undertake a multitude of necessary battlefield roles and provide American warplanners with a major component in their air war. Despite the (rightfully-earned) attention given to the McDonnell F-4 Phantom II), the Thunderchief went on to become a classic American warbird in its own right, produced in volume with a war record to show for its achievements and at the very least, the system bridged a necessary gap between the early years of the Vietnam War and later ones- ultimately paving the way for equally potent aerial hot rods to come.

Factoids
•The Republic F-105 Thunderchief earned the affectionate nickname of "Thud" during its operational life.
• The F-105 Thunderchief became the last aircraft produced by Republic before its merger to Fairchild.
• The Thunderchief accounted for 75% of all air strikes on North Vietnamese ground targets in the first four years of the war.
• The F-105D became the definitive Thunderchief, fitted with a more powerful engine and displaying improved overall performance with production running over 600 examples.

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Last Revision: 9/8/2009