Burbank's sentry stars for the US Air Force

In the late 1940s Lockheed investigated the idea of adapting the Constellation airliner for patrol and airborne early warning duties. The US Navy tacitly recognized the Constellation's potential as an AEW platform, and in late 1948 it ordered two L-749s with AEW radar (BuNos 124437/124438) designated PO-1W, and the first of the two PO-1Ws flew on June 9, 1949. The PO-1W carried large, long-range search radars in massive radomes above and below the fuselage, and the huge amount of side area possessed by the radomes meant that the PO-1W had bigger vertical stabilizers than those of the L-749. Impressed by flight tests of the PO-1W, in the summer of 1950 Lockheed put forward an AEW version of the L-1049 Super Constellation, the L-1049A, and in 1951 the Navy ordered six L-1049As with the designation PO-2W (BuNos 126512/126513, 128323/128326). When the Navy's Bureau of Aeronautics introduced the W-for-Airborne Early Warning aircraft mission category in 1951, the PO-1W and PO-2W were redesignated WV-1 and WV-2 respectively. Deliveries of the WV-2 to Navy electronic warfare units began in 1953, with 136 more WV-2s (BuNos 131387/131392, 135746/135761, 137887/137890, 141289/141333, 143184/143225, 143226/143230, and 145924/145941*) completed. Although airborne early warning versions of the Super Constellation weren't given an official name, Lockheed dubbed them the Warning Star.

*Twenty-two more WV-2s (BuNos 131393/131399 and 145942/145956) were on the US Navy's order books in addition to the first six WV-2s initially designated PO-2W and the other 136 completed WV-2s, but they were cancelled without being built.  

Left: The first RC-121C (serial number 51-3836) in flight, 1955
Right: An EC-121D (serial number 53-0128) in flight with two F-104s, 1958

Even before the first WV-2s began flying, the US Air Force was shopping for an airborne early warning aircraft of its own, and in 1951 it procured ten L-1049Bs originally ordered by the Navy, designating them RC-121C and assigning serial numbers 51-3836/3845 to these aircraft. The RC-121C first flew in 1952 and deliveries to the USAF began in January 1953. A Navy order for 72 WV-2s was also diverted to the Air Force and given the designation RC-121D. The first flight of the RC-121D took place in May 1954 and the deliveries started the following month, with operational deployment of the RC-121D commencing on December 21. Serial numbers 52-3411/3425, 53-533/556, 53-3398/3403, 54-2304/2308 and 55-118/139 were allocated to the RC-121Ds, and one C-121C (serial number 54-183) was converted to an RC-121D. The RC-121C and RC-121D were redesignated EC-121C and EC-121D respectively in 1955. Like the WV-2, the EC-121C and EC-121D were equipped with dorsal and ventral radomes to house the AN/APS-45 height finder and AN/APS-20 search radar respectively, and they could carry a crew of 18 (two pilots, two navigators, two weapons controllers, two flight engineers, one radio operator, two crew chiefs, five radar operators, and two radar technicians). However, in contrast to the EC-121C, the EC-121D had the wingtip tanks of the WV-2 and utilized select equipment changes. The EC-121C and EC-121D were tasked with providing complementary early warning radar coverage to the North Pacific and North Atlantic barriers by flying orbits 300 miles (480 km) offshore from the continental US in what were termed "contiguous barriers", and coverage orbits overlapped those of land-based early warning radars. Three R7V-1s (BuNos 128436, 128438/128439, 131638) acquired by the US Air Force in 1954 were designated TC-121G and reserialled 54-4050/4052 and 54-4058 after being modified to traincrews to fly the EC-121C and EC-121D (serial number 54-4051 would later be converted to a VIP transport and redesignated VC-121G). Two RC/EC-121Cs were lost in accidents, one ditching in San Pablo Bay near San Francisco on November 21, 1953, and another crashing during a flight in rainy weather in Marysville, California, on March 22, 1961, and after the latter accident the remaining EC-121Cs were converted to AEW crew training aircraft and redesignated TC-121C. In 1962, 42 EC-121D airframes and seven ex-USN WV-2s (the latter reserialled 55-5262/55-5268) were redesignated EC-121H after being modified with the SAGE (Semi-Automatic Ground Environment) electronic suite for the AEW role and upgraded new dorsal and ventral radomes housing the APS-103 and APS-95 search radars respectively. The designation EC-121J was assigned to two EC-121Ds (serial numbers 52-3416 and 55-137) modified with additional electronic equipment in the early 1960s, and the US Air Force also acquired three examples of the EC-121P anti-submarine variant of the EC-121K for avionics testing, referring to them as the JEC-121P.

Left: EC-121Ds (serial number 53-3400 in the foreground) at Khorat Royal Thai Air Force Base, Thailand, in 1968. (Courtesy of US Air Force)
Right: An EC-121R on a surveillance mission over Southeast Asia on January 15, 1969. (Courtesy of US Air Force)

After the October 1962 missile crisis, four EC-121Ds of the 966th Airborne Early Warning and Control Squadron based at McRoy AFB near Orlando Florida, were fitted with upgraded electronics and given the designation EC-121Q, and they monitored activities in Cuban airspace and tracked U-2 overflights of Cuba as part of Operation Gold Digger. After the start of Operation Rolling Thunder in March 1965, EC-121s began providing radar early warning and limited airborne control of USAF fighter squadrons fighting North Vietnamese MiGs, and the Big Eye Task Force stationed at the Tan Son Nhut Air Base in Saigon, South Vietnam, was set by the USAF's 552nd Airborne Early Warning and Control Wing to provide support for EC-121Ds making orbits around the Gulf of Tonkin. The first time that the EC-121 successfully used airborne-control interception in the Vietnam War occurred on July 10, 1965, when it provided warning to a pair of F-4C Phantom II jet fighters, which led the F-4Cs to shoot down two North Vietnamese MiG-17s. The Big Eye Task Force relocated to Thailand in 1967 due to the threat of attacks on Tan Son Nhut AB by the Viet Cong and changed its name to the College Eye Task Force, and in April of that year all EC-121s operating with the College Eye Task Force were fitted with QRC-248 IFF transponder interrogators. Back in January 1967, as part of Project Quick Look, the NC-121D (originally designated GRC-121D), which had been built as a WV-2 with BuNo 143226 before being transferred to the US Air Force and given the new serial number 56-6956, was used as a testbed for the QRC-248 system. Beginning in July 1967, the Air Force EC-121s fitted with the QRC-248 system orbited airspace over Laos to provide airborne control of US military aircraft going after Viet Cong activities along the Ho Chi Minh trail. In August 1967, one WV-2 (EC-121K after 1962) originally operated by the Navy with BuNo 143184 and designated EC-121M (not to be confused with the EC-121M ELINT version of the EC-121K) after being acquired by the US Air Force began operational testing of the top-secret Rivet Gym electronics suite (consisting of voice communications intercept stations manned by Vietnamese-speaking intelligence specialists) under Project Rivet Top. After being moved to Korat Royal Thai Air Force Base along with the College Eye Task Force in October 1967, the Rivet Top prototype undertook AEW operations over the Gulf of Tonkin beginning in April 1968, and the EC-121s assigned to the College Eye Task Force were fitted with the Rivet Gym electronics suite the following month. The EC-121R (nicknamed "Batcat") was an EC-121 iteration with ground sensors to detect enemy activities along the Ho Chi Minh trail, and 28 EC-121K/P aircraft and two examples of the WC-121N (WV-3 before 1962) weather reconnaissance aircraft were modified to EC-121Rs after being acquired by the US Air Force in 1966-1967 and assigned serial numbers 67-21471/21500. Painted in the tree-color Southeast Asia camouflage scheme and lacking radomes, the EC-121Rs were deployed to Thailand as part of Operation Igloo White and undertook eavesdropping activities over the Ho Chi Minh trail from October 1967 to December 1971.

Left: An EC-121T (serial number 53-548) (built as an RC/EC-121D) on display at the Yanks Air Museum in Chino, California, photographed by me on July 27, 2022.

The Warning Star that I've seen at the Yanks Air Museum is an example of the last USAF variant of the EC-121, the EC-121T. In the summer of 1970, 22 EC-121D/H aircraft and one EC-121J were fitted with improved electronic systems, namely a digital data receiver, and they were redesignated EC-121T. Many of the EC-121Ts had the dorsal radome and radar removed, but others retained it. On November 12, EC-121Ts began arriving in Thailand from McClellan AFB in California to provide an integrated tactical data display with real-time inputs in support of Operation Kingpin, a mission to rescue US prisoners of war presumably held at the Son Tay prison in Hanoi. The EC-121T would provide radar early warning to jet fighters during the last years of the Vietnam War, especially during Operations Linebacker and Linebacker II, and EC-121Ts with callsign Disco provided radar support while orbiting Laotian airspace and the Gulf of Tonkin in 1971-1972. The last Disco EC-121T mission was flown on August 15, 1973, and the EC-121s stationed at Khorat RTAFB were withdrawn from Southeast Asia on June 1, 1974. The EC-121T was retired from service on March 28, 1975, while the TC-121G would follow suit in June.

In late 1975, the US Air Force began withdrawing the EC-121 from operational service as it prepared to take deliveries of the new jet-powered Boeing E-3 Sentry. All remaining EC-121s were transferred to the US Air Force Reserve's 79th AEWCS at Homestead AFB in Miami-Dade County, Florida, in early 1976, and they continued monitoring Soviet military activities in Cuba until October 1978, when they were retired, ending the quarter-century career of the USAF's Warning Stars.

References:  

Breffort, D., 2006. Lockheed Constellation: From Excalibur to Starliner, Civilian and Military Variants. Paris, France: Histoire and Collections.

Michel, M.L., 1997. Clashes: Air Combat Over North Vietnam 1965–1972. Annapolis, MD: Naval Institute Press.

Winchester, J., 2001. Lockheed Constellation. St. Paul, MN: MBI Publishing.

Transonic all-weather interceptor from Inglewood: the F-86D Sabre Dog

The F-86 Sabre was the most prolific US Air Force air superiority jet fighter built in the 1946-1951 time period, becoming America's chief air combat star of the Korean War by ambushing and fighting MiG-15s in the skies over North Korea. However, it should be noted that the F-86 family itself spawned a variant that would become the second all-weather jet fighter-interceptor to be built in southern California, and this aircraft was originally bestowed a distinct F-for-Fighter designation before being eventually reclassified as an F-86 variant.

The first YF-95/YF-86D prototype (serial number 50-577) on the tarmac at the North American Aviation field near Los Angeles International Airport,

On March 28, 1949, North American Aviation envisaged an all-weather interceptor variant of the F-86 Sabre under the company designation NA-164. The US Air Force showed interest in this proposal, and on April 7 North American itself felt confident enough to undertake engineering work on the production version, to which it applied the designation NA-165. The NA-164/165 differed from the F-86 in having a longer fuselage, a single 7,650 lb (34 kN) thrust General Electric J47-GE-17 turbojet, a clamshell cockpit canopy with a rear hinge, and a 30-inch nose radome on the upper lip of the air intake. The nose radome would carry an AN/APG-36 search radar for interception of enemy aircraft, and because the NA-164/165 was a single-seat aircraft in stark contrast to the F-89 Scorpion and F-94A/B being two-seaters, it required sophisticated electronic systems. Instead of the F-86's four 20-mm cannons, the NA-164/165 itself would be armed with twenty-four 2.75 inch Mighty Mouse unguided air-to-air rockets carried in a retractable tray in the aircraft's belly, although the cannon armament installation of the baseline Sabre was studied as a standby plan. On October 7, 1949, two NA-164 prototypes (serial numbers 50-577/578) and 122 examples of the NA-165 production version (serial numbers 50-455/576) were ordered and the NA-164 was given the designation YF-95 while the designation F-95A was given to the NA-165. The USSR's first successful nuclear weapons test in September 1949 prompted the USAF to order 31 more F-95As (serial numbers 50-704/734), and the YF-95 made its first flight on December 27, 1949. The YF-95 prototypes retained the cockpit canopy, flight controls, and V-shaped windscreen of the F-86A, and the rocket armament and fire-control system were not yet available when flight tests of the YF-95 began.

An F-86D Sabre Dog (serial number 52-3722) in flight 

On July 24, 1950, the F-95 was redesignated F-86D after congressional taxpayers told North American Aviation that funds could be saved if the F-95 were classified as merely an evolutionary development of the Sabre, and thus the YF-95 prototypes became YF-86D. Beginning in September and continuing for two years the Hughes E-3 fire control system was tested aboard the YF-86Ds, and in February 1951 the YF-86D began firing trials of the Mighty Mouse rockets. Deliveries of the F-86D to the US Air Force began in March 1951, and the pressure of the Korean War precipitated an order for 188 F-86D-20-NAs (serial numbers 51-2944/3131) on April 11, 1951, followed by an order for 638 F-86D-25/30/35-NAs (serial numbers 51-5857/6262 and 51-8274/8505) on July 18. Whereas the F-86D-20-NA block had the internal designation NA-177, the latter order (company designation NA-173) was originally designated F-86G when first envisaged in August 1950, differing in having 120-gallon drop tanks for combat missions but ended up being classified as F-86Ds when finalized. Unlike the YF-86D prototypes, the production F-86D had the clamshell canopy, enlarged vertical stabilizer, and a slightly lowered all-flying horizontal stabilizer. The F-86D set a new airspeed record of 698 mph (1,124 km/h) over the Salton Sea in southern California on November 18, 1952, and nine months later, that world airspeed record was shattered on July 16, 1953, when another F-86D flew over the same area at a speed of 716 mph (1,151.8 km/h). The US Air Force was so impressed by the F-86D's performance that yet another production contract for the F-86D was signed on March 6, 1952 for 901 F-86D-40/45/50-NAs (serial numbers 52-3598/4304 and 52-9983/10176), internally designated NA-190, and the final production order was placed on June 12, 1953 for 624 F-86D-55/60-NAs (serials 53-557/1071, 53-3675/3710, and 53-4018/4090), which bore the company designation NA-201. The first 238 F-86D-45-NAs were fitted with the J47-GE-17B turbojet, but the remaining F-86D-45s and all the F-86D-50/55/60-NAs used a more powerful 7,650 lb (34 kN) J47-GE-33 turbojet, which had better cooling and afterburner ignition. The last F-86D was delivered in September 1955, by which time a total of 2,506 F-86Ds (including the prototypes) had been built. The "D" suffix in the F-86D designation led USAF pilots nicknaming this aircraft the Sabre Dog.

In a typical intercept mission, the F-86D's AN/APG-37 radar searched the sky in a forward direction, sweeping back and forth and up and down in a 3.5-second cycle and locating target 30 miles (48 km) away. When the target showed up as a blip on the radar scope, the pilot locked the radar onto the target and the AN/APA-84 computer determined a lead collision course. He flew this course by keeping the steering dot on his scope inside a reference circle. When the automatic tracking system indicated that there were only 20 seconds to go, the pilot steered more precisely to keep the dot in a smaller circle. The pilot chose whether to fire 6, 12, or all 24 of the Mighty Mouse rockets, and pressed the trigger. However, the actual firing instant was determined by the computer, not by the pilot, and when the computer deemed the range to be right, the rocket pack was extended and the rockets were fired. The range at which the computer fired the rockets at the target was typically about 500 yards. It took a half-second for the pack to lower, and only a fifth of a second to fire all 24 rockets. After firing, the rockets fanned out in a predetermined pattern reminiscent of a shotgun blast. When the last rocket was away, the pack automatically retracted back into the fuselage belly, and an "8" appeared on the pilot's scope, warning him that the target was only 260 yards ahead and that he had better break away..

Although the F-86D was the backbone of the USAF's Air Defense Command (ADC) for much of the early-to-mid 1950s, differences among the multitude of operational F-86D production blocks meant that they required different sets of spare parts, different instruction manuals, and different maintenance procedures, leading to maintenance and repair headaches. Therefore, the US Air Force initiated Project Pull-Out in late 1953 to withdraw all F-86Ds built prior to deployment of the F-86D-45-NA production block from operational units and upgrade them to F-86D-45 standard. Upgrades to the early production block F-86Ds included fitting them with braking parachutes and upgraded computer electronics, and when Project Pull-Out was completed in September 1955, a total of 1,128 F-86D-10 to D-40 aircraft had been modified, receiving the designation blocks F-86D-11/16/21/26/31/36/41. Several F-86Ds were deployed overseas to Europe, the Far East, and North Africa beginning in 1954, and in spite of being designed to intercept enemy bombers, the F-86D would never fire a shot in anger against enemy aircraft in its capacity as an interceptor.   

An F-86L (serial number 50-560) on display at the March Field Air Museum, photographed by me in April 2019. This aircraft was one of the first 122 production F-86Ds to be built.

Despite the completion of Project Pull-Out, the F-86Ds were still beset by engine failures and reliability issues with the E-4 fire control system with which they were equipped.  Thus, in the mid-1950s, the US Air Force decided to adapt numerous F-86Ds to use the Semi-Automatic Ground Environment (SAGE) datalink system, which involved use of a large, high-speed ground-based computer for handling and coordinating air surveillance data from various ground radar installations that was transmitted in real-time to a special data receiver aboard the interceptor, and then converted to an on-board system into heading, speed, altitude, target bearing, and range information to guide the pilot in his interception of an enemy aircraft. The first F-86D to have the SAGE system installed flew on December 27, 1955, and beginning in May 1956, under Project Follow-On, it and 575 more F-86Ds were fitted with not only the SAGE system but also extended wingtips and wing leading edges, and engine cooling ducts, resulting in the designation F-86L for these conversions. Thus, the SAGE-equipped F-86D-11 to F-86D-46 aircraft were redesignated F-86L-11 to F-86L-46, whereas the Block 50, 55, and 60 F-86Ds were given the designations F-86L-50 to F-86L-60. The F-86L entered service with the ADC in October, and by this time the ADC had begun withdrawing the F-86D from squadron service beginning in August of that year. Retirement of the F-86D from ADC units was complete by April 1958, and some of the F-86Ds were turned over to the Air National Guard, in which they served until 1961. The F-86L's operational career was rather brief because the deployment of the supersonic F-102 Delta Dagger and F-106 Delta Dart made the F-86L obsolete, leading to retirement of the F-86L from USAF service in 1960. The Air National Guard acquired the F-86L in late 1957 amid the ADC's deployment of the F-102 and F-106, operating F-86Ls until the summer of 1965. From 1958 to 1961, sufficient numbers of retired F-86Ds were exported to Denmark, Greece, Yugoslavia, Turkey, the Philippines, Japan, Taiwan, and South Korea. On the other hand, 17 retired F-86Ls were sold to Thailand in 1964, serving with the Royal Thai Air Force until 1976. In Yugoslav service, F-86Ds were designated L-13 (L stood for Lovac, which means "fighter" in Serbian), and a number of F-86Ds modified for reconnaissance were called IF-86D (with I standing for Izviđač, which is Serbian for "reconnaissance").

A line-up of Fiat-built F-86Ks for the Aeronautica Militare

As the USAF began taking deliveries of the F-86D, America's NATO allies in mainland Europe wanted an all-weather interceptor able to tackle the emerging threat of nuclear-armed Soviet strategic bombers. However, the sophistication of the E-4 fire control system of the F-86D along with its reliability issues meant that exporting the E-4 to US allies was not an option. In response to a USAF request in January 1953 to have Italy operate an interceptor similar in appearance to the F-86D but with cannons, on May 14, 1953, North American conceived an export version of the F-86D, the NA-205, which retained the nose radome radar of the F-86D but was armed with four 20 mm M24A1 cannons designed to operate with a new fire control system designed by North American, the MG-4, which was less technologically complex than the E-4. Two F-86Ds (serial numbers 52-3630 and 52-3804) were selected for the NA-205 project and designated YF-86K, and on May 16, North American signed an agreement with the Italian company Fiat to assemble 50 examples of the production version, the F-86K, which had USAF serials 53-8273/8322 assigned to them although they intended for export to Europe. A batch of 120 F-86Ks to be built for Norway and Netherlands (serial numbers 54-1231/1350; company designation NA-213) was ordered on December 18, and the YF-86K was first flown on July 15, 1954, while the first flight of the production F-86K took place on March 8, 1955, and the first F-86K built under license in Italy flew on May 23. The company designation NA-207 was given to the first batch of F-86Ks built by Fiat, and 171 more F-86Ks (serial numbers 55-4811/4936 and 56-4116/4160) were manufactured under license by Fiat, with North American giving the internal designations NA-221, NA-232, and NA-242 to the latter aircraft. The F-86Ks with the internal designation NA-242 differed from other Fiat-assembled F-86Ks in having slightly increased wingspan and greater wing area. Besides its cannon armament, the F-86K differed from the F-86D in havng a slightly longer nose to house the cannons and ammunition. The US-built F-86Ks (except one retained by the US Air Force were testing) were delivered to Norway and the Netherlands in 1955-1956, and of the 221 F-86Ks license-built by Fiat, 63 were delivered to the Aeronautica Militare, sixty-two went to the French Air Force, and 86 were delivered to West Germany's Luftwaffe, while the Netherlands received six and four were given to Norway. By the 1960s France, Italy, the Netherlands, Norway, and West Germany retired the F-86K from service as the F-104G and Dassault Mirage IIIC entered frontline service, and seventy-four ex-Luftwaffe F-86Ks were sold to Venezuela in 1966 (five of which were later given to the Honduran Air Force in 1969) while 40 F-86Ks previously in Italian service were sold to the Turkish Air Force, which operated them until 1969.