Israel has put an eighth KC-707 aerial refueling aircraft into service. It cost $23 million to convert a Boeing 707 transport into a tanker. Israel introduced the first of these aircraft in 1983, and is in the process of refurbishing the older ones. With these tankers, Israeli F-15s and F-16s can stay in the air longer, and make strikes on distant targets, like Iran. Israel first used the KC-707 to attack Palestinian terrorists, 2,000 kilometers away, in Tunis, Tunisia, in 1985.
The U.S. Air Force introduced a similar aircraft, the KC-135, over fifty years ago. All 732 KC-135s were built between 1956 and 1965. The Boeing 707 commercial transport is actually a civilian version of the original KC-135 (which itself evolved from the World War II B-29 heavy bomber.) Over the decades, the KC-135 fleet has undergone constant repair and reconstruction. New engines, and new structural components have been added, as older items wore out, or showed signs of wearing out faster than anticipated. The problem with older aircraft is that you never know whats going to go next. With current technology, its believed that the KC-135s could be kept going at until 2040. The 145 ton aircraft can carry up to 37 tons of fuel for transfer. Over 500 of them are still in service. The Israeli KC-707 has similar characteristics to the KC-135, but is modified to carry 85 tons of fuel (for itself and for transfer). The KC-707 can also refuel C-130 transports.