During the 1947 Soviet Aviation Day display at Tushino Airport, a surprise appearance was put in by three four-engined long-range strategic bombers. They were early examples of the Tupolev Tu 4, which was a bolt-for-bolt copy of the Boeing B-29 Superfortress, several examples of which had been interned in the Soviet Union after having been forced to land there during bombing raids against Japan. Since the USSR was expected soon to have nuclear weapons, the appearance of the Soviet "Superfortresski" was a shock to US military planners, since it meant that the US mainland might soon be vulnerable to nuclear attack from the air.
The immediate postwar years had left the USAF without any truly modern all-weather fighters to face this new threat. Early attempts to develop jet-powered all-weather fighters ran into a series of snags and delays. The Curtiss XP-87 Blackhawk had been ordered in December of 1945, but it ran into developmental difficulties and the project was eventually totally abandoned in October of 1948. The Northrop P-89 Scorpion was deemed to have greater promise, but it too ran into teething troubles and did not show promise of entering service until 1952 at the earliest. Due to the lack of any suitable jet-powered replacement, the wartime Northrop P-61 Black Widow night fighter was forced to soldier on for a few more years. In order to help fill in the gap until the Scorpion could be available, night fighter adaptations of the piston-engined North American F-82 Twin Mustang were developed and hastily deployed.
The failure of the Curtiss Blackhawk and the delays in the Northrop Scorpion program forced the USAF to consider alternatives. To solve its immediate need for a jet-powered night fighter, in March of 1948 the USAF approached Lockheed with the prospect of fitting its TF-80C two-seat trainer with armament and a Hughes E-1 fire control system. The E-1 system incorporated an AN/APG-33 radar installation coupled with a Sperry A-1C computing gunsight. This system was developed from the AN/APG-3 radar used in the Convair B-36's tail armament. The USAF was in a hurry, and wanted the first production aircraft to be available before the end of 1949.
On October 8, 1948, a General Operational Requirement (GOR) was issued calling for the development of an all-weather interceptor.
Lockheed assigned the company designation of Model 780 to the project. Clarence R. "Kelly" Johnson entrusted the development of the new fighter to a team headed by Russ Daniell. Fortunately, the TF-80C airframe had sufficient volume to house the fire-control system in a modified nose and enough room in the aft cockpit to house the radar operator's position and his associated equipment. Consequently, it appeared at first glance that the adaptation of trainer to night fighter would be relatively straightforward, and the concept was endorsed by the Secretary of Defense on October 14, 1948 which called for the development of the two-seat radar-equipped TF-80C. A Letter of Contract was awarded to Lockheed in January of 1949. The designation F-94 was assigned to the project.
However, early design work soon indicated that the standard Allison J33 of the TF-80C would have insufficient power to accommodate the additional weight of the fire control equipment and armament, resulting in a fighter with a relatively low maximum speed and poor climbing performance. In search of more power, the decision was made to switch to an afterburning version of the Allison J33-A-33, rated at 4400 lb.s.t. dry and 6000 lb.s.t with afterburning. The afterburning engine required a longer and deeper rear fuselage, which pulled the center of gravity to the rear. However, the shift in center of gravity was offset by the weight of the E-1 fire control system installed in a longer forward fuselage and the APG-33 radar set mounted in an upswept nose. An armament of six 0.50-in M-3 machine guns had originally been planned, but space restrictions in the forward fuselage forced the limitation of the armament to only four guns. The guns were mounted in the lower nose section, with their muzzles located just aft of the radome. The air intakes were redesigned and enlarged, the tail surfaces were increased in area, and the internal fuel capacity was reduced to 318 US gallons. However, two 165-gallon under-wing tip tanks could be carried, bring total fuel capacity to 648 US gallons.
Two TF-80Cs (48-356 and 48-373) were modified as prototypes for the F-94 all weather fighter. They were designated ETF-80C, which was later changed to ET-33A when the TF-80C became T-33A. They were unofficially known as YF-94. They initially lacked the radar, the weapons, and most of the operational equipment that was to be fitted to production aircraft. They had the distinctive upturned nose that was to characterize the future F-94A/B, and they featured a frameless T-33-type canopy. Teardrop fuel tanks were mounted underneath the wingtips. The maiden flight took place from the Van Nuys airport on April 16, 1949, with Tony LeVier and Glenn Fulkerson at the controls.
Initial flight tests proved that the handling characteristics were generally satisfactory, but lots of problems cropped up with the afterburner. At that time, afterburners were a relatively new innovation, and there were lots of bugs that had to be ironed out. The engine of the YF-94 suffered from frequent flameouts, often with very difficult relights. These problems were eventually solved by Allison and Lockheed engineers working together to develop a new flame-holder system for the afterburner. The solution to the afterburner problems resulted in the F-94 being cleared for full production and service.
The first production version was the F-94A. One hundred and nine examples had been ordered in January of 1949. Despite reduction of the Air Force budget that occurred as a result of the FY 1949 budgetary crisis, the F-94 procurement quickly rose to 288. The Soviet detonation of an atomic bomb in August 1949 resulted in yet another increase in F-94 procurement to 368 aircraft.
The F-94A was generally similar to the YF-94s, but carried full operational equipment. The seventeen F-94A-1-LOs were practically hand-built models constructed from T-33 airframes taken over from the production line, but the remainder were started on the production line as F-94As. The nose of the F-94A housed four 0/5-inch machine guns with 300 rounds each. The belted ammunition was carried in boxes mounted just head of the cockpit firewall and just behind the avionics boxes. The machine gun armament could be supplemented by a pair of 1000-pound bombs for night bombing missions. A 165 US-gallon teardrop-shaped droptank could be carried underneath each wingtip.
The first F-94A was accepted by the USAF in December of 1949. A total of 109 were built before production switched to the more reliable F-94B model. The F-94A was the first production fighter to be equipped with an afterburner as standard equipment, and it was the first jet-powered all-weather interceptor to serve with the USAF. The F-94A began replacing the North American F-82 Twin Mustangs of the 317th Fighter Interceptor Squadron at McChord AFB in Washington and the 319th Fighter Interceptor Squadron at Moses Lake AFB in Washington in May of 1950.
However, the F-94As proved to be rather troublesome in service, being fraught with engine and electronics problems. The afterburning Allison J-33 engine suffered from frequent turbine blade failures and the fuel system was quite unreliable. The aircraft was unstable and hard to maneuver at high altitude. The pilot and radar operator found that the cockpit was too narrow for them to be able to get in and out of the aircraft quickly during alerts and scrambles. The clearance for the ejection seats was too small, resulting in several tragic accidents during emergency ejections. The fire control radar was quite quirky and unreliable, and the crew members could never be sure that if their system was working at the beginning of a flight that it would still be functional at the end. With the Hughes E-1 fire control system, attacks and firing passes were actually made from the old "pursuit curve" type of attack which resembled a "tail chase" more than a 90-degree, lead collision type of firing pass. The radar gunsight was used to fire at the target aircraft once it was in range. Unfortunately, this exposed the attacking aircraft to the target aircraft's defensive firepower for a rather long period of time.
During service, the early one-piece canopy of the F-94A was replaced by a canopy with a bow frame in the center between the two crew members. This feature was eventually adopted for all subsequent F-94 models as well as on the T-33 trainer. The original under-wing tip tanks were replaced in service by Fletcher centerline tip tanks with a capacity of 230 US gallons each. Some F-94As were fitted with a pod mounted on the leading edge of each wing which carried a pair of 0.50-inch machine guns, bringing the total forward-firing armament to eight machine guns.
The prototype YF-94 (48-356) is on display at Lackland AFB in Texas.
ETF-80C->ET-33A 48-356 and 357 converted to YF-94 49-2479/2495 Lockheed F-94A-1-LO 49-2479/2495 Lockheed F-94A-1-LO 49-2496/2588 Lockheed F-94A-5-LO