Early Vietnam Service – F-101 Voodoo

After the end of the Second World War the USAF needed a suitable escort fighter for the long-range bomber fleet of Strategic Air Command. The F-101, developed in the mid-1950s by the McDonnell Aircraft Company from their prototype XF-88 Voodoo, fitted the bill. The maiden flight took place on 29 September 1954, but the official commissioning into the air force was delayed until the spring of 1957.

The F-101 was part of the so-called “Century” series (F-100 to F-110). Its powerful J57 Pratt & Whitney engine with after-burner gave the aircraft a top speed of around 1900 km/hr with a range of 2,900 km, but as these fell short of the required performance parameters it was decided to arm the F-101 fleet with a cannon and nuclear missile and from then on use it as a fighter-bomber. Later NORAD (North American Aerospace Defense Command) also used Voodoo units for interceptor operations and patrol flights over North America. The F-101 served in other roles including as RF-101A photographic reconnaissance with cameras in a modified nose. F-101 reconnaissaince units flew many operations for the Air National Guard during the Cuba crisis and in Viet Nam.

The F-101 was used by the United States Airforce and the Canadian Royal Air Force. The F-101 saw many unique roles in its 20+ year career. Originally designed to be a fighter-bomber, the aircraft quickly moved on into reconnaissance and continued to serve as a “utility infielder” of sorts with interception duties and a training role. Unfortunately, despite some of its advanced capabilities and its speed (for the time), there was a nasty little aerodynamic issue which caused the aircraft had a serious “pitch-up” problem that while improved, was never fully fixed.

Pitch-up is a type of aggravated stall that commonly occurs in aircraft of this wing type. An aircraft can stall at any time if the AOA is exceeded.  In this case though, pitchup could occur and cause stability issues that actually would lead to a stall. The pitch-up was caused by downwash on the stabilizer during high AOA that causes both a pitch up from the downward force and a reduction in the effectiveness of the stabilizer itself.  Essentially, the jet would become unstable.

The pitch-up tendency was actual double wammy against stable flight. If uncorrected, this issue could cause departure from controlled flight. Luckily, the Air Force was aware of these problems and created training videos concerning what needed to be done to correct the issue mid-flight. This video was put together to train pilots how to avoid the envelope where pitch-up was most likely to occur.

Now it’s easy to look back on these early training videos and think how boring it must have been to watch them.  But put yourself in the position of the crew for a moment. Here you were about to fly one of the most advanced fighters of the day and you were being told that if you exceed seemingly normal AOA’s, you could depart controlled flight and not be able to recover.  It would make me pay attention. That’s for sure!

Early Vietnam

By February 1965, provocative Viet Cong attacks on US facilities at Pleiku AB, near Saigon, made the use of escalating reprisal strikes politically inevitable. For USAF RF-101 pilots, this involved one of the most crucial missions of the war – finding the enemy and conveying that information to control centres for it to be converted into targets. The combat environment in which this task was to be performed could hardly have been more challenging.

The Voodoo was one of the first US jet aircraft to participate in the Vietnam War. RF-101As of the 17th TRS had visited the area in 1957-58, and Voodoos were intended to replace the RF-84F Thunderflashes of the 67th TRW’s 15th TRS `Cotton Pickers’ at Kadena and the 45th TRS `Polka Dots’ at Misawa AB on the island of Honshu, Japan, whose aircraft began to arrive in mid-1958. A USAF comparative evaluation showed that the RF-101’s superior speed and the versatility of its camera equipment gave it a major operational advantage over the RF-84F. Nevertheless, the Thunderflash had a useful camera suite and long range, and in late 1962 Thirteenth Air Force asked unsuccessfully for eight to supplement its limited RF-101C numbers. Requests for one or two additional RF-101Cs were also denied, as the other USAF commands hung on to their scarce Voodoos. It was not until 1 April 1963 that two more 45th TRS aircraft joined the Operation Able Mable team in Thailand, bringing its total strength to just six Voodoos.

From March 1960 the 15th TRS was attached to the 18th TFW, which was part of the 313th Air Division, while the 45th TRS was assigned to the 39th Air Division so that the 67th TRW could be deactivated that same year. Their vast operational area of interest covered Japan, Korea and Southeast Asia down as far as South Vietnam, so long high-altitude transit flights were commonplace. Fortunately, the Voodoo’s cockpit was comfortable by fighter standards. Pilots sometimes photographed Soviet bombers, patrol aircraft and intelligence-gathering ships. Very precise navigation was required, assisted by TACAN, an ARA-25 direction finder and an AN/ASN-6 navigation computer, but dependent mainly on piloting skills. In-flight refuelling became essential for most missions, and RF-101Cs were well-equipped for that, having been designed at a time when the USAF was transitioning from drogue-trailing KB-50s and KC-97s to flying boom-equipped KC-135A Stratotankers. An extending refuelling probe could plug into a drogue basket, or a receptacle mid-way along the top of the fuselage could accept a Stratotanker’s boom.

The deployed Voodoos soon suffered from corrosion due to the salt-laden air around their coastal bases and extensive re-skinning was required, both at their airfields and during depot maintenance and modification at Hill AFB, Utah. Like other bare metal-finished aircraft of the time, they were eventually given a protective coat of Air Defense Command Aircraft Gray (FS 16473) paint, before eventually being camouflaged for Vietnam operations. Corrosion, particularly of magnesium components, would continue to plague RF-101Cs located in the humid climate of Thailand and South Vietnam. A new corrosion control facility had to be established at Kadena to tackle these problems as 15th and 45th TRS aircraft rotated through temporary deployments.

Weather was another enemy, but in the form of thick sea fog, tornados and tropical storms, rather than the standard European low visibility. RF-101s from the `Cotton Pickers’ had to seek alternative bases on several occasions due to typhoon warnings, and one aircraft was lost in heavy cloud when the squadron had to divert to Itazuke AB, Japan. Its pilot, Capt Lavender, ejected over the sea and was drowned when his parachute dragged him below the surface of the water.

Increasing tensions in Southeast Asia generated a series of requests for reconnaissance detachments to operate from bases in Thailand and South Vietnam. Initially, the Geneva Conventions’ ban on the use of US jet aircraft in South Vietnam had to be circumvented by training Vietnamese Air Force (VNAF) pilots to fly Lockheed RT-33 reconnaissance/ trainers. Also, Project Field Goal (using camera-equipped ex-Philippines Air Force RT-33 53-5347 as a `one-man reconnaissance wing’) at Don Muang, Exercise Air Bull and Project Pipe Stem were short-term commitments leading to the creation of the Able Mable Task Force in 1961. Camera-equipped C-47B 44-76330 of the 315th Air Division also briefly operated out of Udorn RTAFB until it was shot down by Pathet Lao ground fire on 23 March 1961, killing seven of its eight crew (the sole survivor was held as a PoW for 17 months).

The overall aim of these reconnaissance missions was to monitor North Vietnamese military support for communist Pathet Lao forces that were preventing the establishment of a neutral, unified Laos. Four RF-101Cs visited Don Muang for two days in June 1960 to provide reconnaissance for the Thai government and three more deployed to Takhli RTAFB for the first nine days of March 1961 for Southeast Asia Treaty Organisation (SEATO) Exercise Air Bull without significant political fall-out over Geneva Conventions violations, so the plan to train VNAF reconnaissance pilots was quickly dropped.

The first longer-term detachment of four Voodoos to Don Muang was approved by the Thai government in October 1961, and on the 18th of that same month four RF-101Cs and six pilots from the 15th TRS arrived at Tan Son Nhut AB near Saigon, ostensibly for an airshow appearance. The shortage of ground-support facilities and fuel meant that KB-50 tankers had to be used to ground-refuel the Voodoos by attaching their in-flight refuelling baskets to the fighters’ extended refuelling probes. Although the airshow never happened, the RF-101Cs stayed at the base as the Pipe Stem Task Force, with its own support personnel and photo processing cell (PPC) that would soon be flooded with miles of photographs whose main content was top-views of forest. Nevertheless, Pipe Stem Voodoos provided the USA with the first hard evidence in 1962 of North Vietnamese and Pathet Lao activity in northern Laos. The photographs, taken by Capt John Evans, were flown directly to the White House for analysis.

A rationale was devised for the Voodoos to stay in place for a month as the only jet reconnaissance force in the area. The Mekong River had burst its banks on the day the Voodoos arrived, making 320,000 people homeless and causing widespread damage, so the South Vietnamese government requested photo-reconnaissance of the affected areas. These flights commenced on 20 October, followed 24 hours later by the first Pipe Stem sorties. During the latter, Voodoos flew covert reconnaissance missions over the Plain of Jars, the Ho Chi Minh Trail and northern Laos, where Soviet supply aircraft and troops were photographed (with the RF-101C’s 36-inch split vertical cameras) assisting the Pathet Lao and North Vietnamese forces. The photographs provided Washington with the first clear evidence of this intervention. The flights quickly began to attract ground fire as the RF-101C gradually entered into the conflict and the detachment required reinforcement.

Pipe Stem came to an end after 67 useful sorties that demonstrated the effectiveness of tactical reconnaissance by fast jets like the RF-101C. Officially, the International Control Commission (ICC) had allowed it into the area temporarily to photograph flood damage by the Mekong River, and when the floods abated the ICC ordered the detachment back to Kadena on 21 November. Although the jets returned to Okinawa, the ground support equipment (some of it acquired from USAFE units) remained in place for an expanded Able Mable force, with Tan Son Nhut AB later established as Operating Location 2 for the RF-101C’s activities.

On 7 November 1961 a 45-man detachment from the 45th TRS commanded by Maj Ken Harbst and including a PPC run by the 67th Reconnaissance Technical Squadron (RTS) took up residence at crowded Don Muang for Project Able Mable – a 30-day arrangement that would replace the RT-33 Field Goal effort which had ended in mid-May. The PPC was established in an abandoned barracks at the run-down base, water supplies for photo processing were arranged and two A9 processing machines were flown in, although they proved to be so troublesome when used that much of the vast film footage generated by the Voodoos initially had to be hand-processed. Humidity, poor-quality film emulsions and insect invasions all added to the daily workload. Doug Ayers, a 460th TRW film technician, recalled that these local processing problems persisted into the mid-1960s;

`Film damage often happened due to power loss because the diesel fuel was of poor quality and the plumbing lines would get clogged because of a build-up of silver [photographic residue] in them. I figured that this [residue] could exceed 20,000 ounces per month, but I’m not sure if that included the 40,000 lbs [of film stock] a month that was burned as scrap, including about 120 ounces of silver per 1000 lbs of film.’

All the pilots had considerable experience of the Voodoo, most of them having flown it in USAFE. Very different tactics would be needed in Southeast Asia, however. Their medium-altitude RF-101C flights – usually up to three per day – covered the Laotian and South Vietnamese Ho Chi Minh Trail supply routes to Viet Cong insurgents at a tactical radius of up to 500 miles from Don Muang. They were met by truck-mounted quad 0.50-cal or 23 mm automatic fire and accurate, heavy AAA in a few areas such as Tchepone at altitudes up to 40,000 ft. Maj Herbst’s aircraft was hit over South Vietnam, knocking out an engine and wounding the pilot, although he managed to land at Don Muang.

Mission planning was a late-afternoon routine based on orders received from PACAF HQ and requiring the selection of several targets for each RF-101C sortie. Pilots were supposed to perform their missions at 40,000 ft to disguise their presence over a supposedly neutral country, although many flights took place at lower levels, particularly when the unpredictable weather ruled out the use of high-altitude cameras. Lower flights attracted small-arms fire, and several aircraft returned with bullet holes after making photo passes below 1500 ft, prompting a short-lived instruction to use minimum altitudes above 5000 ft. Choke point areas on the trails network were most likely to have AAA defences. In the summer of 1961 Voodoos photographed 23 Soviet-built PT-76 amphibious light tanks moving on the supposedly neutral Plain of Jars.

Most missions were flown over Laos but an increasing number covered targets in northern South Vietnam and (occasionally) Cambodia in a covert programme called French Leave, which often forced pilots at the full extent of their range to divert to Tan Son Nhut for refuelling and processing of their film.

As the Viet Cong insurgency increased throughout 1961, so demands on the Able Mable crews also grew and their 30-day stay was extended, rotating pilots and aircraft at six-week intervals. The combat experience gained at this time by 45th TRS pilots, who were flying up to 20 sorties each during a typical deployment, was invaluable for their widening role in the war. By the time Able Mable over Laos came to an end in December 1962 (much to the displeasure of the USAF) in order to comply with neutrality agreements, the RF-101Cs had flown 720 missions over Laos and South Vietnam. However, President Kennedy subsequently sanctioned further Able Mable flights over South Vietnam.