WikipediaIran Air Force F 4 Phantom II interceptor fighter bomber.
In late November Iran carried out a series of airstrikes close to its border with Iraq against ISIS. Although the airstrikes are already notable for signaling possible military coordination between Iran and the US, they become even more notable in light of Iran's choice of aircraft.
Iran provided air support to the Iraqi military and the Kurdish Peshmerga with its ageing fleet of F-4 Phantoms. The Phantom, which first flew in 1958, was originally used by the US Navy as an interceptor, used to track down and destroy enemy aircraft. However, the plane was adopted by the Air Force and Marines for every conceivable combat and training role and was exported to 11 other nations. 
Under the Shah's reign, Iran was actually one of the US's most reliable allies in the Middle East before the Islamic Revolution in 1979. Iran bought 225 F-4 Phantoms in the 1970s. And although the majority of these once state-of-the-art planes have become inoperable due to age and damage sustained during the 1980s Iran-Iraq War, Tehran still manages to keep several dozen of the planes operational. 
The maintenance of the fighters has been a challenge due to ongoing sanctions against Tehran. Spare parts for the Phantoms had to either be smuggled into Iran, cannibalized from other fighters, or replaced with a parts reverse-engineered by the Iranians themselves. This has led to a steady degradation in the number and quality of aircraft that Iran can field while at least allowing them to keep a number of US-built fighter jets on hand.Iran F-4 PhantomsShahram Sharifi
Against an enemy like ISIS, even four-and-half-decade-old F-4 Phantoms are more than capable. Since ISIS lacks any semblance of a capable air defenses, older planes like the Phantom can be used to great effect as long as Iran has access to solid on-the-ground intelligence.
The Phantom still can carry a punch as a bomber as well. The plane can carry up to 18,650 pounds of weapons including general-purpose bombs, cluster bombs, guided bombs, and air-to-ground missiles. 
Iran is still looking for a domestically produced alternative to their aging American aircraft. Although they're of lower quality than what's produced in the US and Europe, sanctions have forced the Iranians to develop a domestic defense industry capable of bu idling battleships, drones,ballistic missiles, and submarines — something that no other country in the region can boast.
They want to do the same with fighter aircraft: the Saeqeh, basically a reverse-engineered F-5, may have entered operational service in September of 2010, although it's unknown how many have actually been built.
Even with a domestically built fighter plane, Iran is still sending the F-4 into combat. And it's not alone in continuing to use the Phantom. Turkey still maintains its fleet of F-4s, and Germany only just retired their Phantom fleet in 2013. But the aircraft last saw action with the US military during Operation Desert Storm, over 20 years ago.
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