Profile- Boeing’s Jet Heritage, Pt III

The three VC-137As were ideal Presidential and VIP transports and the aircraft immediately commenced flying in this somewhat unique role for which converted C-135s were not considered good enough; all three remain in service. Initially powered by turbojets, the aircraft were re-engined during the early 1960s with JT3D turbofans and therefore were redesignated VC-1378s.

Following the initial three VC-137NBs was the VC-137C, a 707-3208 series airframe designed to fulfil a similar role as the A model. Two VC-137Cs were acquired during the mid 1960s and took up their posts as Air Force One airborne presidential command posts, remaining in this highly specialised role until replaced in late 1990 by Boeing 747-200 series aircraft. The VC-137Cs contained a similar layout to the earlier NB models, though with their longer fuselage could carry an even greater array of communications equipment and additional passengers. Such is the importance of the Air Force One requirements, that at least one aircraft had to be airborne at all times.

However the VC-137 was an extraordinary example of military 707 transports, because most such aircraft were not so highly modified for such a specialist communications and VIP transport role. Amongst the first military users of the aircraft in the transport role was the West German Luftwaffe, which purchased four 707-320Cs direct from Boeing in the mid 1960s, all of which are still in service. Since the 1960s, more air forces worldwide have acquired 707s for the transport role, most acquiring ex-civilian examples during the 1970s and 1980s, though others such as the Canadian Armed Forces have also purchased the type direct from Boeing insmall numbers. Amongst operators of ex-civilian 707s in the transport role is the Royal Australian Air Force, which purchased an initial two 707-338s (VH-EAD and -EAG) from Qantas when the airline retired the type, and commenced operating the aircraft as VIP/transport aircraft; four additional 707-320C series aircraft have been acquired for tanker conversion.

Tanker development

Whilst the KC-135 has remained the prime air refuelling asset of the US Air Force, the 707 has also been adapted to provide an air-to-air refuelling capability for several air forces worldwide, and as such has even been used on operational missions, most recently in the Gulf war with the Royal Saudi Air Force.

The first military service to utilise the 707 airframe for tanker operations was the Canadian Armed Forces (CAF), which in the late 1960s decided to replace its aging fleet of 12 Canadair CC-106 Yukon tanker/transports with jet aircraft. The CAF (like Israel and Iran at about the same time) sought to acquire the KC-135 for the role, however Boeing’s Renton production line had already closed and the USAF could spare none from its inventory. The CAF was eventually swayed by the Luftwaffe’s success with its four transports so opted to purchase the 707, acquiring five which were already on the production line as a result of a cancelled airline order. The first aircraft, which were designated CC-137 in line with the USAF designation for its VIP 707s, arrived in April 1970.

Two of the five CC-137s were converted to tankers soon after their completion, carrying removable Beech 1080 hose-and-drogue refuelling pods under each wingtip, typically enabling two CF-5s (and now two CF-18 Hornets) to refuel simultaneously. Modifications included extending the wing spars to support the additional weight of the refuelling pods, the wingtip magnetic compass flux valves were relocated to the vertical fin, and additional exterior lighting was installed to better illuminate the aircraft during refuelling operations. Two special observer stations were positioned at the rear of the fuselage.

Testing began in May 1971 with the Royal Air Force, and by the end of 1972 both designated tankers had been fully equipped for refuelling operations, proving so successful that by 1977 additional 707 tankers were being requested, but despite repeated requests and recommendations, budget restrictions have meant that no further 707s have been acquired by the CAF and none of the three transport aircraft have been converted to tankers. The five Canadian CC-137s are expected to remain in service until at least 2010.

Besides Canada, both Iran and Israel also expressed interest in the KC-135, however they too were forced to acquire 707s for refuelling purposes. The pre-revolution Iranian Imperial Air Force its first 707 tanker in 1974, being unique amongst 707 tanker operators in having KC-135 type ‘flying boom’ refuelling equipment installed for compatibility with F-4 Phantoms. When Iran acquired the Grumman F-14 Tomcat in the mid 1970s, the 707s were then also fitted with Beech 1080 hose-and-drogue equipment, providing a unique refuelling capability for the type. The aircraft proved useful during the eight year Iran-Iraq war, however it is not known how many, if any, remain in service.

Boeing itself has actively marketed the 707 tanker concept, and partly as a result of this no less than 12 nations have adopted the aircraft as tankers. Besides Canada and Iran, the air arms of Australia, Brazil, Israel, Italy, Morocco, Peru, Saudi Arabia, South Africa, Spain and the US Navy have placed the 707 into service as tankers. The aircraft is therefore seeing extensive service in the refuelling role, and has even been operated successfully in a combat environment. The Israeli Defence Force (IDF) has utilised its 707 tankers (as well as modified electronics warfare aircraft) over Lebanon, and used another 707 as command aircraft for the daring 1976 Entebbe raid. The single Moroccan aircraft has also reportedly been used on operations, though details remain sketchy.

The Saudi KE-3As were routinely flown in operations in support of Saudi aircraft protecting shipping during the protracted Iran-Iraq war, whilst during the more recent Desert Storm operation the aircraft again proved their worth when they flew alongside US and French KC-135s, refuelling mainly Saudi aircraft in the battle against Iraq. Unlike most other 707 tanker aircraft however, the eight Saudi KE-3As are not in fact direct developments of the 707, but instead derivatives of the 707 development the E-3 Sentry (described later in text) Australia has purchased four ex-civilian 707-320Cs for conversion to tanker aircraft and the first was officially handed over in mid April this year. The four RAAF aircraft will utilise refuelling equipment developed by Israel Aircraft Industries, similar to equipment already in service with the IDF’s 707 tankers. The aircraft uses Flight Refuelling Ltd (UK) developed refuelling pods, in particular Mk. 328 pods, of which the RAAF is the first operational user. Besides the installation of the pods near the wingtips, the RAAF tanker modification involves avionics upgrades and the installation of specialist equipment, such as a viewing camera in the lower rear fuselage for the flight engineer to use during refuelling operations. An individual aircraft will be capable of refuelling up to six F/A-18 Hornets during one mission. (Refer p. 54 May 90 AA for an in-depth description of the RAAF 707 tanker upgrade and mods involved. )

Sentry AWACS

Whilst 707 tankers continue to prove their worth to armed forces worldwide, it is as AWACS (Airborne Warning and Control System) aircraft that the military 707s have really come into their own. Unlike the tankers, which are in the main modified 707s originally built to civilian specification, the E-3 AWACS aircraft are purpose built utilising airframes direct from Boeing’s production line.

The need for an effective jet powered AWACS aircraft became apparent during the late 1960s, and during the early 1970s two prototype aircraft (designated EC-137D) based on 707-3208 air-frames were evaluated, final development testing being completed by the end of 1976.

The Boeing E-3 Sentry AWACS was developed as a mobile, flexible, survivable and jamming resistant high capacity airborne radar station, command post and communications centre. Offering long range surveillance of both high and low altitude aircraft in all weather and above all terrain types, the aircraft has become an essential element of Western defence. It can be used for a variety of missions without necessitating changes in equipment configurations, providing real time assessment of enemy action and/or the identification and positioning of friendly aircraft. Later models and aircraft with updated equipment also have maritime identification and assessment capability.

In USAF service, the Sentry has two main operational uses: to act as a command and control centre to support quick reaction deployment and tactical operations by Tactical Air Command aircraft: and to operate as a survivable early warning airborne command and control centre for the identification, surveillance and tracking of enemy aircraft, and to command and control their interception. The Sentry’s effective surveillance radius is 200nm for low flying fighter sized aircraft, and even further for aircraft at higher altitudes.

Several externally similar E-3 Sentry variants have been built for the USAF, NATO, Saudi Arabia, France and Britain. Sentry production has brought the number of 707 airframes produced to a final total of 1,010; any future customers will have to utilise modified ex-civilian 707s for their AWACS requirements. The two prototype EC-137Ds were followed by the first 24 production Sentrys for the USAF, designated (Core) E-3A. These aircraft were equipped with pulse-Doppler radar for high and low alti- tude aircraft tracking: IBM CC-1 computer; nine situation display consoles (SDCs), which provide the mission crew with all information for effective surveillance operations; two auxiliary dis- play units (ADUs) to support communications, maintenance and data processing; and 13 available communications links (seven UHF, three VHF/AM, one VHF/FM and two HF/SSB). Twenty-four aircraft (the two EC- 137Ds and 22 Core E-3As) are now being updated to E-3B standard with the installation of ECM-resistant voice communications; one more HF and five more UHF radios; a new and faster CC-2 computer; five more SDCs; a Westinghouse-developed maritime surveillance capability; and Have Quick anti-jamming provisions.

NineUSAF aircraft and the 18 NATO aircraft were completed to the (US/NATO Standard) E-3A configuration, essentially similar to the Core E-3A but with a full maritime surveillance capability; CC-2 computer; additional HF radios; ECM-resistant voice communications; radio teletypewriter; and provisions for self defence and ECM. Both the Core and US/NATO Standard aircraft are more commonly referred to as simply E-3A. The US/NATO Standard aircraft are being updated to E-3C standard with five additional SDCs, five more VHF radios and provision for Have Quick anti-jamming improvements.

In 198 1the sale of five E-3A AWACS and six E-3 derivative tankers (designated KE-3A) to Saudi Arabia was approved. Options for these aircraft have been exercised and the aircraft have been in Saudi service since 1986 and operated alongside USAF Sentrys during Desert Storm. Just as the USAF and NATO aircraft are being updated, the Saudis are now discussing updating their Sentry fleet with new computers, Global Positioning System, improved radar and communications equipment, and a self defence capability. Further E-3 sales have been made to France (E-3F) and Britain (E-3D Sentry AEW. 1), and both have now entered service with their respective air forces, though deliveries of the final aircraft are continuing. Unlike the USAF and NATO aircraft, which are powered by Pratt & Whitney F33-PW- 100turbofans, the Saudi, French and British aircraft are powered by CFM56 turbofans.

During the latter years of the Cold War and more recently during the Gulf war, the E-3 Sentry well proved its worth with the surveillance of aircraft and the control and command of Allied aircraft. In the Gulf the Sentry tracked Iraqi aircraft from the start of the invasion of Kuwait and throughout Desert Shield. During Desert Storm itself, the aircraft were responsible for tracking Iraqi aircraft and, perhaps more importantly, for the control of Allied aircraft attacking Iraqi positions and undertaking combat air patrols. The Sentrys also remained on station for the surveillance of Iraqi aircraft during the cease fire period, in which at least two Iraqi aircraft were shot down by USAF fighters.

Joint-STARS

Also proving valuable during the Gulf Wacwas the USAF’s Grumman E-8A Joint-STARS (Joint Surveillance Target Attack Radar System), which despite being still in its development test program made its operational debut in the Gulf War.

The primary duty of the E-8A Joint-STARS, which is being developed by Grumman for the USAF’s Electronics Systems Division, is to detect stationary military vehicles and to track moving vehicles, such as tanks, on or near the battlefield; the aircraft itself operates in comparative safety some distance from the frontline. The E-8 employs both synthetic aperture radar and Doppler systems for surveillance of ground targets, information about which it transmits to either Army or Air Force ground sta tions. Air Force attack aircraft can then be directed to the armoured vehicles, which may have remained hidden were it not for the aircraft’s systems. Based on a 707-320C airframe, the aircraft’s most noticeable external modification is the installation of its 7. 93m (26ft) long radome mounted under the forward fuselage and housing a large multimode, phased array radar.

Two prototype Joint-STARS aircraft were operationally tested during the Gulf war, and have been highly praised for performing to all expectations. The aircraft were extensively tested in the three weeks leading up to their operational deployment on 11 January, the first aircraft flying an operational sortie 12 hours prior to the commencement of Desert Storm on 17 January. While routinely flying behind Allied lines, the aircraft could detect tank and troop movements up to 200km away, though they could not differentiate between tracked and wheeled vehicles; this will be rectified by the end of the development phase. The US military were extremely satisfied with the Joint-STARS performance, which gave commanders additional, vital information for effective battlefield management. On 22 January the aircraft made possible an air strike in which 58 Iraqi tanks were destroyed; at the battle of Khafji J-STARS confirmed that the Iraqis were not moving up reinforcements, information of great value to the field commanders; at least one mobile Scud missile unit was detected by the J-STARS aircraft. Twenty E-8 Joint-STARS aircraft will ultimately enter service with the USAF.

Tacamo

In April 1983 Boeing was contracted to develop a survivable airborne communications system based on the 707 airframe to provide an on-station/all-ocean link between the US National Command Authorities and the US Navy’s Trident ballistic nuclear submarine fleet. To be designated E-6A Tacamo (TAke Charge And Move Out), the aircraft were destined to replace the EC-130Q Hercules fleet already used in this role. At the time of writing, ten of the 16 aircraft on order were in service, operating as an airborne communications relay system for the USN submarine fleet, using mainly low frequency radio signals transmission for the task.

T he E-6A’s airframe is externally similar to the E-3A Sentry (minus the large tracking rotodome) with which it retains 75% systems commonality, though like the British and French Sentrys the E-6 is powered by military versions of the CFM56 turbofan. The Tacamo’s interior is divided into three main functional areas: forward of the wings, the four crew flight deck and crew rest areas, described as 50% common with the E-3A; centre compartment with food storage, galley, dining area, toilets, and an eight bunk rest area for relief crew carried on extended or remote deployment missions; the C3 overwing compartment contains communications equipment and operators, while to the rear are the radio transmission racks, transmitters, trailing wire antennae and reels, equipment spares, parachutes and a bailout door.

The prototype E-6 Tacamo made its first flight in February 1987 and full flight testing commenced in July of that year after the aircraft’s specialist avionics equipment had been installed. The fleet was initially intended to operate on a 24 hour flying basis, however this is currently under review to determine whether communications to patrolling USN submarines can be maintained with reduced flying hours. Currently two US Navy squadrons operate the E-6A Tacamo from Maryland and Hawaii, however from June 1992 all aircraft will be home based at Tinker AFB, Oklahoma.

And so the 707 has gained renewed value as an airframe because of its military use worldwide as tankers, transports and electronic warfare aircraft. The aircraft are expected to remain in service with military operators well into the next century, probably outflying civilian counterparts which are progressively reducing in numbers (now remaining mainly as cargo transports and specialist corporate and charter aircraft) as the military fleet grows and expands to operate in a wide range of vital defence roles.