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.
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