There are some big tanker aircraft flying around the world, including those based on the DC-10, 767 and Russia's IL-76 design. Yet the largest aerial refueler of them all is based on the iconic Boeing 747, a symbol of American might and ingenuity. Ironically, it flies for none other than the Islamic Republic of Iran Air Force.
The 747 heavy tanker-transport concept evolved out of a mid-1960s USAF initiative to field a much larger tanker than the plentiful Boeing 707 derived KC-135 Stratotanker. Eventually this movement would result in the Advanced Tanker-Cargo Aircraft program, otherwise known as the ATCA.
By the mid 1970s, the USAF selected two primary designs out of four ATCA contenders. The original four were the DC-10, the Lockheed L-1011, the Lockheed C-5 and the Boeing 747. The resulting two finalists were the DC-10 and the 747. The C-5 was dropped because it was simply too large and too expensive for the mission, while a cargo variant of the L-1011 had not been produced yet, so its design was considered too risky seeing as the similarly configured tri-jet DC-10 was already available in a cargo optimized version.
The first Boeing 747 ever built was adapted to test the "KC-747," otherwise known as the KC-25 in USAF parlance, boom configuration which was very closely modeled on the tried and true flying boom used on the KC-135 Stratotanker. Testing occurred with various receivers, including the SR-71 Blackbird, and the KC-747/KC-25 proved to be a fantastically stable and capable platform.
In its final production configuration, the KC-747 would have had its own aerial refueling receptacle on its nose, as seen on the 747 based E-4 airborne command post, which was put into service around the same time as the KC-25's development. The jet would also have featured a tilt-up cargo nose for easy loading and unloading of large cargo, and there were even designs for a self deployable ramp for rolling wheeled and tracked vehicles on and off the Jumbo Jet without the use of a lift.
There would also have been major fuel tank modifications and some tweaks to the boom system to enhance its operating envelope based on an ongoing (at the time) USAF study into a "next generation boom."
Although the KC-747 could haul more weight and volume than the KC-10, and offer more fuel for passing to other aircraft (over 100k lbs more, a whole KC-135 worth) along with greater endurance, the KC-10 was cheaper to purchase and to operate.
At the time the USAF had higher monetary priorities than the ATCA and the potential of buying more airframes on a set budget was enticing. Additionally the KC-10 had some unique features, one being its "fly-by-wire" advanced boom system, which had a much larger envelope than the KC-747s initial boom configuration.
The KC-10 also featured some automated break-away features that were fairly novel at the time, all of which could have been added to a final production version of the KC-25 incidentally. Runway length was also a major sticking point of the USAF's parameters, the KC-10 could operate from shorter runways under certain weight configurations than the KC-747/KC-25.
By 1977 the KC-10 "Extender" was chosen by the USAF to fulfill its heavy tanker requirement, of which 60 examples were produced, with another pair of similarly modified DC-10s being purchased by the Royal Netherlands Air Force. Years later another pair of "KDC-10s" would also be converted for use by commercial contractors Omega and Global Air Services.
Even though the USAF went with KC-10, the whole KC-747 concept was not a total loss, with two of these aircraft being procured by the Shah of Iran while the whole ATCA selection program was still underway. These aircraft were primary procured by Iran for cargo duties, along with ten other non-aerial refueling capable 747s. At the time the Shah had hundreds of F-4 Phantoms on order and the KC-747 could pass hundreds of thousands of pounds of fuel to an armada of these fighters alongside their less capable KC-707 sister tankers. In fact many more of KC-747s were on the Shah's weapons wish list before he was deposed in 1979.
Fast forward almost four decades, and the KC-747 still soldiers on in Iranian service today, although one of the two tankers was lost during a thunderstorm years ago, so just a single KC-747 remains in service.
The fact that the Iranian Air Force still flies the world's only KC-747 just adds to the reality that Iran, with its hodgepodge of antique Cold War era American and Soviet aircraft, along with its dated Chinese imports and ex-Iraqi "refugee" jets, continues to possess the ability to put on the planet's most marvelous "throw back" air show.
Just seeing an F-14 Tomcat beat up the overhead landing pattern one more time would be well worth the plane ticket itself, yet alone seeing a functioning KC-747 fly overhead while being flanked by desert camouflaged F-4 Phantoms. So please do all of us military aviation dorks a favor, and pray for peace in the Middle East, so that we can fly metaphorically back in time to see Iran's retro air force up close and personal, KC-747 included.
Photo credits Boeing and Public domain
Tyler Rogoway is a defense journalist and photographer that maintains the website Foxtrot Alpha for Jalopnik.com You can reach Tyler with story ideas or direct comments regarding this or any other defense topic via the email address Tyler@Jalopnik.com