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| RSAF KC-135R 752 at Darwin Airport 2010. Photo : Eugene Butler via Wikimedia Commons |
The Republic of Singapore Air Force ( RSAF ) has been operating a quartet of ex-USAF Boeing KC-135R Stratotankers since 1999. Though their main mission is to extend the range and endurance of combat aircrafts through aerial refueling, they are also capable of transporting cargo and personnel and can be configured for aero-medical evacuation.
They play an absolutely crucial role in supporting the overseas deployment of the RSAF's fighters and in just about any of the Singapore Armed Forces' ( SAF ) training deployments in foreign nations. They have also been participating in peacekeeping missions and in humanitarian assistance and disaster relief ( HADR ) operations on a regular basis.
However, with an average age of 56 years, the entire RSAF KC-135 fleet will soon be replaced by six Airbus A330 Multi-role Tanker Transport ( MRTT ), the first of which had already been delivered in August 2018. In this all-you-may-want-to-know article we review the history of the Stratotanker and its almost two decades of operation in the RSAF, before they are all gone. But first, some snippets of Boeing lore.
Origins And Development
In the early 1950s, the Strategic Air Command ( SAC ) of the USAF began operating jet-powered strategic bombers such as the B-47 that flew faster and higher than their predecessors. The accompanying aerial tanker fleet however were still entirely populated by piston-engine aircrafts like the KB-29P and KB-97 that were not only unable to match the performance of the jet bombers but also used fuel that were incompatible with jet aircrafts ( aviation gasoline vs kerosene ) requiring a separate tanking system for transferrable fuel.
At around the same time Boeing's intention to develop an all new jetliner had generated little interest from the civil aviation industry whose members were still unfamiliar with jet transports and were rather contented with the success they had operating piston-engine aircrafts.
Believing that the requirement for a jet-powered tanker by the USAF was inevitable and that the best way to convince the airlines on the viability of the jetliner was to have a working example, Boeing started work in secrecy on a new long range jet prototype for the tanker / transport role that could also be adapted into an airliner. It would be known as the Model 367-80 or the Dash 80.
Boeing would end up investing US$16 million, representing two-thirds of the company's net profits from the post war years, for the construction of the prototype. It was an enormous risk for Boeing as there were no committed customers at that time. The Dash 80 achieved first flight on 15th Jul 1954, two years after project launch. Boeing would later reveal that when the prototype was almost finished, the company took another gamble by tooling and gearing up for a production aircraft, even though neither the Air Force nor any airline had placed a single order.
The gamble paid off handsomely when in 1954 the USAF deemed it urgently needed 800 jet tankers to fuel its new B-52 bomber fleet which was then on the brink of entering service. The initial order of 29 tankers came in barely three weeks after the prototype's first flight, long before it had done any inflight refueling tests! It would be designated as the KC-135 Stratotanker. In the following year, despite not winning the SAC's design competition for a jet tanker, Boeing would receive an interim order of 250 tankers since its proposal was already flying and could be delivered two years ahead of the winning Lockheed design. Eventually, the Air Force decided against supporting two tanker types and the Lockheed order was dropped entirely.
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| The Boeing Model 367-80 prototype from which the KC-135 and the 707 jetliner evolved. Photo : Wikipedia |
The Boeing KC-135 Stratotanker
The production version KC-135A Stratotanker would differ only in minor respects from the original Dash 80 prototype while the hugely successful Boeing 707 jetliner developed in a parallel program called for a totally fresh design with a wider fuselage, fatigue resistant airframe of 2024 aluminium alloy and completely revised systems. This would explain why the KC-135 and the B707 looked rather identical in external appearance but we know that the similarity is only skin deep!
The KC-135s were built and assembled at Boeing's plant at Renton, Washington. This same facility also built the B-29 Stratofortress and later the KC-97. In fact, the first production KC-135 nicknamed " The City of Renton " shared the tarmac at Renton with the last KC-97, symbolizing the complete conversion to jet-power by Boeing ( see image below ).
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| Roll-out ceremony of the first production KC-135A at Boeing's Renton plant. On the tarmac is the last KC-97. Photo : Boeing / AMC / USAF |
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| The first of the 732 production KC-135A s/n 55-3118 aka The City of Renton was retired in 1998 after decades of service and more than 40 years after its first flight. It is now displayed near the east gate of McConnell AFB, Kansas. USAF photo |
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| Another view of KC-135A 55-3118 at McConnell AFB with a B-47 in the background. Interestingly, this aircraft never perform any aerial refueling missions but was instead deployed to escort fighters from state side to Vietnam, used as a command and control platform for Tactical Air Command and even as a VIP transport for Dr Henry Kissinger's secret trip to Beijing in 1971. USAF Photo |
The first flight of the KC-135 was achieved on 31st Aug 1956 with deliveries beginning on 30th April 1957. Thus the KC-135 became the USAF's first jet-powered refueling tanker and has been in active service for more than six decades and counting.
Originally intended to refuel strategic nuclear-capable bombers, the KC-135 would later be extensively used to increase the range and endurance of combat fighters and tactical bombers. Boeing claimed that KC-135s made a total of 813000 aerial refueling in 9 years during the Vietnam War while 278 million pounds of fuel were transferred in 18700 refueling during the Gulf War.
A total of 820 aircrafts of the C-135 family were built at Renton before production ceased in 1965. The peak production rate was a frenzy 20 aircrafts per month. Of those 732 were tanker configurations while 88 were modified for special purposes including cargo carriers, reconnaissance, airborne command post and VIP transport.
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| The original mission of the KC-135 was to refuel strategic bombers such as this B-52. Photo : Wikimedia Commons |
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| The KC-135A would later be used extensively to refuel tactical aircrafts like the F-4C during the Vietnam War. Monochrome Photo : USAF |
The KC-135 Variants / Modifications
This section covers the main variants of the KC-135 and omits the small numbers of special missions modifications like the KC-135Q/T for supporting SR-71 operations or the KC-135B, KC-135D and NKC-135 test beds. It uncovers how the R model came about and the subsequent upgrades made.
KC-135A
The KC-135s were originally powered by the Pratt and Whitney J57-P-59W turbojet engine which was not known for reliability, fuel efficiency nor quietness. These were designated the KC-135A. The J-57 was relatively underpowered and a special technique known as water injection has to be applied to temporarily boost the engine output during take-off especially when the aircraft was fully loaded. Problems with the J-57, in particular insufficient thrust and engine failure, was listed as the cause of many KC-135 accidents and crashes in its initial few years of operations.
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| The KC-135A is powered by turbojets that are cigar-shaped and had nacelles with rather smooth outlines. USAF Photo |
KC-135E
The first major modification program in the 1980s retrofitted 157 KC-135A with the Pratt and Whitney TF-33-PW-102 turbofan engine from retired Boeing 707 jetliners which resulted in an improvement in fuel efficiency and an increase in the amount of fuel deliverable. These re-engined aircrafts were designated the KC-135E. The USAF had retired the last KC-135E in 2009 which meant Chile is now the sole remaining operator of the type.
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| The KC-135E is powered by early generation turbofans which are still slender looking but the nacelles have a slightly larger diameter anteriorly giving a stepped appearance. Photo : USAF |
KC-135R
A second modification retrofitted several hundred KC-135A and some KC-135E with new CFM56-2 high bypass turbofan engines from CFM International which produced significantly higher thrust and better fuel efficiency. The upgraded aircrafts were then designated as the KC-135R. The USAF received its first KC-135R in 1984. Compared with the original KC-135A version, the KC-135R is 25% more fuel efficient and could off load 50% more fuel to receiver aircrafts on a medium radius mission. They also cost 25% less to operate and are very much quieter. The new turbofans are also capable of producing more than double the thrust of the older turbojets and thus reduce the runway take-off requirements by 2400ft.
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| The KC-135R is powered by high bypass turbofans with their characteristic short and fat nacelles. Photo : USAF |
Pacer CRAG / Block 30
Subsequently, the avionics of all KC-135 in the USAF inventory then numbering about 560 were modernized under the US$700million Pacer CRAG ( compass, radar and global positioning system ) program by Rockwell Collins from 1996 to 2002. Upgraded avionics included cockpit enhancement with an integrated flight management system, liquid crystal flat panel multifunction display, forward-looking predictive windshear weather radar, traffic collision avoidance system and an enhanced ground proximity warning system. The fuel management system was also upgraded. This upgrade would also reduce the flight crew number from three to two, largely eliminating the requirement for a navigator. The Block 30 upgrade which was performed concurrently with Pacer CRAG further rectified some minor deficiencies.
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| This was how the cockpit looked like before Pacer CRAG enhancement. Photo above shows the co-pilot at the controls of a KC-135Q during Operation Desert Shield. The KC-135Q is a special variant of the KC-135A that has a separate fuel system for carrying the JP-7 fuel for the SR-71 Blackbird. USAF |
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| Cockpit of a KC-135 participating in RIMPAC 2010. It should have undergone the Pacer CRAG upgrade program which was completed by 2002. Photo : USAF |
GATM / Block 35
Further modernization of the communication and navigation systems were carried out in support of the global air traffic management ( GATM ) initiative to allow the KC-135 to operate over civil airspace. The so called Block 35 GATM upgrade involved 544 aircrafts and was worth US$700million. Rockwell Collins was awarded the contract in 1999 and managed to complete the entire project on time in 2011 with very little cost growth, one of the rare success stories in the aviation industry.
Block 45
Beginning around 2010, the latest and ongoing US$910 million Block 45 modernization builds on the Pacer CRAG enhancements to convert the 1950s era tanker to a truly modern digital platform of the 21st century. It upgrades or replaces 63 items including analog instruments that are redundant or considered high-maintenance. The KC-135 will receive a new autopilot, a digital flight director, radar altimeter and a large-format color digital engine instrument display.
The Block 45 upgrade relied heavily on the use of commercial off-the-shelf equipment or systems to both reduce costs and simplify the modification process. As a result, the upgrade only required on average between 50 to 55 days for completion. The program had delivered the 45th upgraded KC-135 by the end of 2016. The current plan is to have all the KC-135s upgraded to Block 45 standard by 2024.
The Block 45 upgrade was implemented despite the fact that the replacement for the KC-135, the Boeing KC-46A Pegasus is about to be introduced into service with the USAF. In reality the projected KC-46 buy stands at 179 aircrafts and is hugely insufficient to replace the entire active KC-135 fleet of 396 aircrafts ( Active Duty 153, Air National Guard 171, Air Force Reserve 72 ). So some KC-135 tankers will have to remain in service, perhaps until the 2040 fiscal year, maybe even a decade after that, according to the USAF.
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| KC-135R Block 45 after ( left ) and before ( right ) instrument panel. Photo : Air Mobility Command / USAF |
KC-135 International Customers
Apart from the USAF, the KC-135 had been exported to several international allies of the United States :
The French Air Force - 11 x C-135FR Direct Commercial Sale Mar 1962
- 3 x KC-135R Foreign Military Sale ( FMS ) Jun 1997
The Turkish Air Force - 7 x KC-135R FMS Dec 1997
The Republic of Singapore Air Force - 4 x KC-135R FMS Sep 1997
The Chilean Air Force 3 x KC-135E FMS Feb 2010
Aerial Refueling And The RSAF
It would seem not unreasonable to question why a small country like Singapore would require aerial refueling capability for its air force. After all, unlike the SAC which at the height of the Cold War had to maintain fleets of doomsday bombers on 24 hour airborne alert or the US military which seemed to be constantly involved in supporting one operation after another somewhere in the world, Singapore is at peace with its neighbours and has no ambition to expand its sovereign territory.
The truth is that being a highly urbanized small island nation of approximately 700 square kilometers, land-scarce Singapore has to conduct a significant amount of its military training overseas, especially for the Air Force and the Army. The Singapore Armed Forces regularly trained in countries like Brunei, Thailand, Australia, Germany and Taiwan while the Air Force has detachments in Australia and France for flight training and the United States of America for helicopter and fighter training. The Air Force also regularly participated in multinational exercises like Ex Pitchblack, Ex Cope Tiger and the Red Flag / Maple Flag series in the US and Canada. The SAF also actively contributed towards United Nations peacekeeping missions and disaster relief operations.
All these overseas training and missions carry with them huge logistic demands as equipment, supplies and personnel need to be transported to and from the host country. Without a competent air mobility arm some of these army training on foreign soil would simply be impossible. In addition, fighter deployments especially those involving longer distances would require aerial tanker support to avoid staging multiple refueling stops which can be costly and time consuming.
Prior to the acquisition of the KC-135R in 1997, the RSAF already had four KC-130B and one KC-130H tanker transport aircrafts. The KC-130Bs were converted C-130B freighters and not purpose built tankers. The modifications were done locally by ST Aerospace. The KC-130B/H utilized the drogue and probe refueling method and did not have the refueling boom to cater to receptacle equipped aircrafts. It was adequate to refuel the probe equipped A-4SU and the F-5S but it cannot refuel the newer receptacle equipped F-16A/B which were acquired in ever increasing numbers beginning from 1985. Since the KC-130B/H are turboprop driven, there was again the performance mismatch between the tankers and the receivers. It was these requirements for aerial refueling, especially the need for the flying boom system that prompted the search for a new jet-tanker to augment the KC-130B/Hs.
Tanker Selection
With a mixed population of probe and receptacle equipped fighter aircrafts in the nineties, it would not be hard to understand that the RSAF's new tanker should be equipped with both the probe-drogue system and the flying boom system, like the McDonnell Douglas KC-10 Extender. I do not believe there were many choices then when it came to a duel-system long range jet-tanker. Modern options like the A310 MRTT, A330 MRTT, KC-767 simply did not exist in those days. Of course one could always consider conversions from used or new airliners, like the Boeing 737 but events in the nineties presented opportunities that probably made the options of buying new tankers or converting old freighters unattractive.
The collapse of the Soviet Union in 1991 and the end of the Cold War lead to the successive closure of several hundred US military bases and installations in a process known as Base Realignment and Closure ( BRAC ). Much of these were SAC bomber bases that hosted strategic bombers and their accompanying aerial tankers. Entire refueling squadrons and bombardment wings were made redundant and their personnel and equipment either redistributed among surviving establishments or forcefully retired, until finally even the SAC itself could not escape being disestablished as a major command in 1992.
As a result of BRAC which was actually implemented in several rounds from 1988 until the year 2005, many of the KC-135 tankers comprising mainly of the original A versions that were not upgraded were put into long term storage at the Davis-Monthan Air Force Base in the boneyard managed by Air Force Materiel Command's Aerospace Maintenance and Regeneration Center ( AMARC ). These retired KC-135A airframes had on average flown only a fraction of their estimated 36,000 flight hours service life. They could be taken out of storage, refurbished and continue active service for many more years. Because they were Air Force surpluses, they could be had for a reasonable sum, assuming the US government was willing to sell them.
As it turned out, in September 1997 under the Peace Guardian foreign military sale program, the RSAF acquired four such KC-135A to be re-engined to the KC-135R standard before delivery. The tankers would also receive the Multi-Point Refueling System ( MPRS ) modification at the same time to enable drogue and probe refueling in addition to the standard boom method.
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| KC-135A 63-8016 at AMARC in a photo taken in Jun 1994. This aircraft would be subsequently sold to Singapore under FMS in 1997. Photo used with the kind permission of K West 1 via Flickr |
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| This is likely how the RSAF's KC-135Rs would look like before they were refurbished. Photo above shows KC-135A s/n 57-2592 preserved at Davis-Monthan AFB. Wikimedia Commons |
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| Spraying protective sealant on the tail of a KC-135E in preparation for preservation and storage at AMARC. Photo : USAF |
Modernizing RSAF's KC-135
The chosen aircrafts were taken out of AMARC storage and were sent to the Oklahoma City Air Logistics Center, Tinker AFB for processing. The Boeing Company was selected to modernize the KC-135As. Upgrading works was carried out by the Military Programs - Wichita Division at the facilities in Wichita, Kansas where the old polluting and noisy J-57-P-59W turbojets were swapped for new reliable and fuel-efficient CFM56-2B turbofans. The MPRS installation with the Flight Refueling Limited Mk32B wing mounted hose and reel pods was done concurrently.** The delivery of the upgraded KC-135Rs took place between 1999 and 2000.
The avionics would have been modernized separately upon the delivery and return of the tankers in Singapore. An upgrade package equivalent to the Pacer CRAG enhancement was subsequently carried out by the local aerospace company ST Aerospace.
According to the SIPRI arms transfer database the FMS deal was possibly worth US$280 to US$500 million. This was likely the total sum which would have included the cost of spares, training, basing arrangement and perhaps even aircraft leasing. Then, the cost of each new CFM-56-2B engine was about US$8million while the fabrication and assembly of the re-engine kit which included new engine struts and nacelles, structural fittings and wiring harnesses, cost about US$4million per aircraft.
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| RSAF KC-135R at Ex Pitchblack 2018, Darwin, Australia. The Mk 32 pod clearly visible near the wingtip. Photo : RAAF |
The Peace Guardian Detachment
It would be of no use for any air force to own jet tankers if they did not know how to operate them effectively. Therefore from July 1998 to 2003, the RSAF maintained a 300-person detachment at McConnell AFB in Kansas under a basing arrangement that would allow the RSAF to train with the USAF in jet tanking operations. The Letter of Offer and Acceptance for the training program which were to be valid for 25 years, was signed in March 1998. Using leased KC-135R the RSAF's Peace Guardian Detachment trained with the 350th Air Refueling Squadron to hone their skills on air refueling techniques, tactics and general airmanship while waiting for the delivery of their own tankers.
Those pioneer group of airmen would form the core of the RSAF's 112 Squadron which was inaugurated in December 2000. The KC-135Rs would eventually return to Singapore and operate out of Changi Air Base. 112 Squadron achieved full operational capability by August 2002, a remarkable feat made possible only because of the high quality training the Peace Guardian Detachment received from the USAF.
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| Emblem of the 350th ARS |
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| Training with the best : The air refueling wing at McConnell AFB is the world's largest with 62 KC-135 stratotankers. Photo : AMC / USAF |
Mission Capabilities
The KC-135R has an maximum take-off weight of 322500 pounds ( 146285kg ) and a maximum transfer fuel load of 200000 pounds ( 90719kg ). It has a maximum cargo payload of 83000 pounds ( 37648kg ) and can take up to 80 passengers.
It has a range of 1500miles ( 2419km ) with 150000 pounds of transfer fuel and a ferry range of 11015miles ( 17766km ). Since the KC-135R burns approximately 10000 pounds of fuel for every hour of flight and regulations require a minimum landing fuel of 25000 pounds, it can also mean that with the maximum load of 200000 pounds there would be about 95000 pounds of fuel available for transfer during a standard 8 hour mission.
The KC-135R's main method of fuel transfer to receiver aircrafts is through its rigid flying boom. A boom operator controls the maneuverable boom from the small compartment know as the boom pod at the rear of the tanker. The boom can deliver a maximum of 6000 pounds of fuel per minute when all four air refueling pumps of the tanker are activated during topping up of large aircrafts like the C-17 Globemaster. For fighter aircrafts however, the usual transfer rate is less than 1500 pounds per minute for smaller single engine aircrafts and less than 3000 pounds per minute for larger twin engine aircrafts as their fuel systems are not designed to withstand the high delivery pressures.
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| KC-135R of the 434th ARW with boom deployed at the Louisville Air Show, Kentucky, 21 Apr 2018 USAF Photo |
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| Business end of the boom. KC-135R 927th ARW soars after refueling a C-17 1 Jul 2014. USAF Photo. |
In addition to the standard flying boom refueling method common to all KC-135s, the RSAF's KC-135R can refuel two probe equipped aircrafts concurrently using its two MPRS wing pods, provided that the wingspan of the receivers do not exceed 68 feet ( 21.7m ). It can also refuel receptacle equipped aircrafts with the aerial boom during the same mission. This multi-system arrangement adds a lot of flexibility compared with the standard boom-only KC-135R which forms the bulk of the USAF fleet. Boom-only KC-135s must have a boom-drogue adaptor attached to the boom to refuel probe equipped aircrafts and while doing so cannot service receptacle equipped aircrafts during the same mission.
With the retirement of the F-5S and the A-4SU, the requirement for refueling with the hose and drogue method within the RSAF has been greatly reduced as the current F-16C/D and F-15SG fighters utilize the aerial boom method for refueling. The MPRS is however still highly relevant during overseas missions in support of coalition aircrafts which might be probe equipped, like US Navy and Marine Corps fighters and most of the tactical aircrafts of European origin.
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| KC-135R with MPRS such as this tanker assigned to the 380th Air Refueling Wing can refuel two probe equipped aircrafts concurrently. Photo : USN |
However, unlike the newer tankers like the KC-10 Extender, the KC-46 Pegasus and the A330 MRTT, the RSAF's KC-135R are not receiver-capable. In other words, they are able to offload but cannot receive fuel when in the air. Though the USAF has a fleet of eight receiver-capable stratotankers known as the KC-135RT for Special Operations missions, they are far too valuable an asset to retire or divest in a foreign military sale to Singapore or any country for that matter.
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| A receiver capable USAF KC-135RT with the receptacle above the cockpit is being refueled by another KC-135 over Kansas in June 2016. Photo : AMC / USAF |
For airlift missions, the upper deck of the KC-135R can be quickly configured to carry passengers, cargo or litters for medical evacuation. The KC-135R can take 6 standard pallets and all kinds of rolled on cargo including jet engines. A large cargo door facilitates loading and unloading.
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| A large cargo door facilitates off-loading of humanitarian supplies during an Air Force Reserve training mission at Ramstein AB Germany Dec 2012. Photo : USAF |
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| The cargo deck can be configured to carry litters for medevac missions. USAF Photo |
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| The cargo deck configured as troop carrier. Photo : USAF |
Operational History in the RSAF
In close to two decades of active service within the RSAF, the KC-135R fleet had participated in numerous missions and exercises overseas. Listed are some notable missions :
28th Mar 2000 A KC-135R from the Peace Guardian Detachment refueled four RSAF F-16C/D fighters for their flight to Singapore from Cannon AFB, New Mexico. The distance between Singapore and New Mexico is greater than 16000km. This marked the first time a RSAF KC-135R had conducted mid-air refueling for its own aircrafts. On 5th Apr 2000, the KC-135R made the journey back to rejoin the Peace Guardian Detachment based at McConnell AFB, Wichita.
5th Nov 2000 A KC-135R conducted an aeromedical evacuation mission to bring back to Singapore three casualties from the Singapore Airlines SQ006 crash at Taipei, Taiwan.
7th Jan 2005 The Indian Ocean Tsunami that resulted from a magnitude 9 earthquake off the coast of Aceh in Indonesia on 26th Dec 2004 killed a total of 230000 people in 14 countries. As part of the SAF's HADR effort known as Operation Flying Eagle, a KC-135R was tasked to ferry the then United Nations Secretary General Mr Kofi Annan and his 20 member delegation from Medan, Indonesia, to the various tsunami affected countries in order to gain an overview of the relief effort. Technicians at Singapore Technologies Aerospace were given only 3 days to convert the KC-135R into a VVIP carrier. Airliner seats were bolted to the cabin floor which was then carpeted over. A table with reading lamp was added so that the Secretary General could work onboard the aircraft. Stopovers were made in Sri Lanka, the Maldives and Mauritius.
23rd Feb 2011 A KC-135R spearheaded the disaster relief effort for the Christchurch earthquake in New Zealand ferrying the advance party of the earthquake-relief team ahead of a slower RSAF C-130 transport. 32 civilians were evacuated to Auckland. The distance between Singapore and Christchurch is more than 8400km.
From May 2015 The RSAF had periodic deployments of a KC-135R tanker to support air-to-air refueling operations in the Defeat-ISIS coalition. The tankers had been deployed three times to Al Udeid, Qatar, on three month detachments. During a deployment, the KC-135R could carry out more than 50 missions, refueling an average of four to six aircrafts per sortie. They refuel allied fighters attacking Daesh targets in Iraq and Syria in support of Operation Inherent Resolve.
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| RSAF KC-135R of 112 Sqn operating out of Al Udeid Air Base refuels a USAF F-15E in support of Operation Inherent Resolve. Photo RSAF via USAF |
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| RSAF KC-135R 751 sits on the flight line at Al Udeid Air Base next to a USAF Stratotanker on 23 May 2017. Photo USAF |
10th Oct 2017 A KC-135R delivered humanitarian aid worth about US$200000 to Bangladesh to provide relief to the displaced people escaping from the ongoing genocide / ethnic cleansing in neighbouring Rakhine State of Myanmar. The mission was carried out over two days.
Some of the large-scale multi-national air combat exercises involving the RSAF's KC-135R are listed here :
Exercise Cope Tiger, Korat AFB, Thailand. This is an annual series aimed at improving combat readiness and interoperability between the Republic of Singapore Air Force, Royal Thai Air Force, and U.S. Air Force. Cope Tiger 2018 involved 58 aircraft, 39 Ground-Based Air Defence (GBAD) systems, and about 1,300 personnel from the participating nations. The RSAF participated with six F-15SG and six F-16C/D fighter aircraft, one G550 Airborne Early Warning aircraft, one KC-135R Stratotanker, four GBAD systems and approximately 380 personnel.
Exercise Pitch Black, RAAF Base Darwin and Tindal. This is a biennial series on offensive and defensive counter air combat in a simulated war environment which the RSAF had participated in since 1990. The RSAF deployed five F-15SG, six F-16C/D, a KC-135R Stratotanker and a G550 Airborne Early Warning aircraft in Pitch Black 2018. This year’s exercise was the largest ever, with 140 aircrafts and up to 4,000 personnel from 16 participating nations, taking place in training areas larger than that of the Red Flag series.
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| RSAF KC-135R leading JAS-39, F-16 and F-15 in Cope Tiger 2018 Photo RSAF via FB |
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| RSAF KC-135R at Darwin Airport for Pitch Black 2018. Photo : RAAF |
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| RSAF KC-135 refueling RAAF F-111C off the coast of Darwin in Pitch Black 2004. Photo : RAAF via Wikimedia Commons |
Historical Aircraft Data
The RSAF's four KC-135R had each completed close to three decades of active service in the USAF as KC-135As before being withdrawn from use and put into storage at AMARC. I am sure they each have their own interesting service history rotating through different units and supporting the many missions of the Air Force all over the globe. However, after all these years, information pertaining to the history of each individual aircraft can be extremely fragmented and difficult to obtain. The last unit which they were assigned with is indicated under the remarks column. Much of what is shown below can be obtained from the unofficial AMARC website here.
| USAF Serial Number | MSN | LN | RSAF | First Flight | Deliver Date | Re-skin | AMARC PCN | AMARC Arrival | AMARC Departure | Remarks |
| 59-1454 | 17942 | 357 | 752 | 22.1.60 | 9.2.60 | Jan-84 | AACA0083 | 1.9.93 | 19.6.98 | 906th ARS / 43rd ARW, Scott AFB, IL* |
| 61-0325 | 18232 | 547 | 751 | 25.9.62 | 5.10.62 | Aug-87 | AACA0091 | 29.9.93 | 12.12.97 | 93rd ARS / 398th Ops Grp Fairchild AFB, WA* |
| 63-8009 | 18626 | 665 | 750 | 6.12.63 | 20.12.63 | Sep-87 | AACA0073 | 26.7.93 | 1.8.97 | 46th ARS / 305th ARW, McGuire AFB, NJ* |
| 63-8016 | 18633 | 672 | 753 | 16.1.64 | 28.1.64 | Apr-85 | AACA0099 | 12.5.94 | 18.11.98 | 93rd ARS / 398th Ops Grp Fairchild AFB, WA* |
Note :
US military aircraft serial number - First two digits indicates fiscal year in which the aircraft was procured
MSN - Boeing's Manufacturer Serial Number
LN - Line Number
PCN - AMARC's now defunct Process Control Number
Here are some photographs of the KC-135s before and after their transfer to the RSAF.
KC-135R s/n 750
KC-135R s/n 750 with USAF registration number 63-8009 was operated by the 46th Air Refueling Squadron, 410th Bombardment Wing, based at K.I. Sawyer AFB, Michigan. Between 1 Jun 1992 to 8 Oct 1993 when it was inactivated, the 46th ARS was attached to the 305th Operations Group. The aircraft was withdrawn from service on 26 Jul 1993. The 305th OG is currently based at McGuire AFB, New Jersey, which is shown on the AMARC Experience database above. Of all the four KC-135s in the inventory of the RSAF, old USAF era photographs of 750 is the hardest to find. In fact I have not managed to find any.
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| RSAF KC-135R s/n 750 in 2010 Photo : Aldo Bidini via Wikimedia Commons |
KC-135R s/n 751
KC-135R s/n 751 with USAF registration number 61-0325 most likely could have been operated by the 42nd Air Refueling Squadron operating out of Loring AFB, Maine, as seen in the photo below. The 42nd ARS was inactivated on 1 Sep 1991 while the aircraft could have been reassigned to the 93rd ARS, 398th Operations Group, Castle AFB for another 2 years of service before being retired to AMARC on 29 Sep 1993.
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| KC-135A 61-0325 ( 751 ) was assigned to the 42nd ARS operating out of Loring AFB, Maine. This photo was taken on 24.6.89 at RAF Mildenhall. Photo : Used with the kind permission of Phil Cossey via ABPic.com |
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| RSAF KC-135R s/n 751 at Avalon Airport in 2001. Photo : David Pryde via Wikipedia |
KC-135R s/n 752
KC-135R s/n 752 with USAF tail number 59-1454 is the oldest among RSAF's four Stratotankers. It was operated by the 906th Air Refueling Squadron, 43rd Operations Group based at Minot AFB, North Dakota. The 906th ARS supported combat operations in South East Asia between 1968 to 1975, participating in Operation Young Tiger and supporting Operation Arc Light. The aircraft was sent to AMARC on 1 Sep 1993. 906th ARS operated out of Minot AFB until 1994 when it was transferred to Grand Forks AFB and then finally to Scott AFB, Illinois from 2009. This could explain why in the AMARC Experience database the aircraft's last unit was listed as 906th ARS / 43rd ARW Scott AFB instead of Minot AFB.
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| KC-135A 59-1454 ( RSAF 752 ) refueling a USAF EB-66 Destroyer in S.E. Asia in the sixties. Photo : Wikipedia |
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| KC-135A 59-1454 ( RSAF 752 ) at RAF Mildenhall 5th Jun 1993, 3 months before retirement to AMARC. Photo used with the kind permission of Paul via Flickr Paul pslg05896 |
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| RSAF KC-135R s/n 752 as it was in 2011 Photo :Aldo Bidini via wikicommons |
KC-135R s/n 753
Old photographs of KC-135R s/n 753 taken at the International Air Tattoo held at Boscombe Down in 1992 ( see below ) showed KC-135A 63-8016 with the famous Triangle K insignia which indicated that it was operated by the 379th Bombardment Wing based at Wurtsmith AFB, Michigan. With the closure of Wurtsmith AFB on 30th Jun 1993 as a result of the BRAC process, the aircraft could have been reassigned to the 93rd Air Refueling Squadron, 398th Operations Group, then based at Castle AFB, California. It was mothballed on 12th May 1994. Castle AFB was itself closed on 31st Mar 1995 and the 93rd ARS was relocated to Fairchild AFB, Washington. This could explain why the AMARC Experience database listed the aircraft's last unit as 93rd ARS / 398th OG Fairchild AFB, instead of Castle AFB, clearly a discrepancy.
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| KC-135A 63-8016 ( RSAF 753 ) at Boscombe Down, UK 14th Jun 1992. Photo used with the kind permission of Kerry Taylor via Flickr |
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| RSAF KC-135R s/n 753 as it was in 2011. Photo : Aldo Bidini via Wikimedia Commons |
Final Words
Aerial refueling could perhaps be considered one of the greatest game changer in the history of modern air warfare. Initially conceived to extend the strike range of strategic bombers as well as their loiter time during airborne alert patrols, its role has now been extended service wide to enhance the war fighting capabilities of all kinds of tactical aircrafts. The frequently quoted adage Nobody Kicks Ass Without Tanker Gas ( NKAWTG ) probably carried with it a lot of truth. If there is any single name that is synonymous with aerial refueling, it has to be the KC-135 Stratotanker. Not only is it the world's first jet tanker, it is also the most numerous and is still in active service in the USAF and four other air forces worldwide after more than six decades. The C-135 airframe was also the basis for subsequent platforms such as the EC-135 and RC-135.
However, with increasing age comes spiraling maintenance costs and reduced readiness and availability. While the RSAF and the French Air Force can look forward to the replacement of their entire KC-135 fleets with the Airbus A330 MRTT within the next few years, the USAF struggles on with its KC-X / KC-46A program.
In his book Voices From An Old Warrior - Why KC-135 Safety Matters, author Christopher J.B. Hoctor stated the official USAF estimates of the replacement cost of a KC-135 at US$3.6 million in 1956, $5 million in 1960, $10 million in 1973, $17.3 million in 1986, $20.1 million in 1989 and $40 million in 2013. He alleges that there exists not many more KC-135 airframes at the boneyard that can be converted into an operational R model within a reasonable time and budget. Today, an operational KC-135R with its crew is a priceless asset that is irreplaceable ... at least for a few more years.
I wonder what the RSAF would do with its KC-135R fleet when they are retired from service. It will not be easy to preserve such large airframes in land scarce Singapore whether in the Air Force Museum or as an airbase gate guard. Back to Davis-Monthan AFB for long term storage again perhaps? Who knows the USAF might be interested to reacquire them in a reverse FMS - Foreign Military Buy Back?!
** Despite the claim by Boeing that the engine upgrade and the MPRS installation were done concurrently at its Wichita facilities before the KC-135s were delivered, I have reason to believe that this may not apply to all four of RSAF's KC-135R.
An ex-ST Aerospace employee revealed to me that he was previously involved in the MPRS installation of two KC-135 in Singapore sometime around 2001 or earlier. Unfortunately, he could not remember the serial numbers of the aircrafts he worked on. He mentioned that the most challenging part of the MPRS installation was the electrical cabling works where miles of wires have to be trunked through confined spaces. The control panel where all the connections had to pass through was physically located behind the toilet compartment ... and dealing with all the old insulation materials made his skin itchy and he wondered if it could have contained asbestos, not improbable as the aircrafts were all constructed more than 50 years ago where the carcinogenic properties of asbestos have just been discovered.
