AN Australian air force tanker jet has come to the rescue of a US F/A-18 Hornet experiencing difficulties over northern Iraq.

The RAAF KC-30A tanker was diverted to refuel the United States Marine Corps fighter after it experienced engine troubles during a combat mission against the Islamic State.

Australia has deployed six of its own Hornets along with the tanker and an E-7A Wedgetail airborne early warning and control aircraft to Iraq and Syria as part of an international coalition against the Islamic State.

Mechanical failure forced the US F/A-18 Hornet pilot to shut down one of its two engines..

This placed greater strain on its remaining engine — causing it to burn up more fuel than expected for its long journey home.

Refuelling the crippled aircraft posed a challenge.

“A challenging feat at the best of times, air-to-air refuelling with an engine-out Hornet had only ever been conducted in flight testing scenarios and never before from the RAAF aircraft over a war-zone,” a Department of Defense statement reads.

The Hornet had also dropped bombs from one of its wings — making the aircraft even less stable.

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“The hardest part was that the Hornet couldn’t maintain the required altitude or speed that we normally refuel at due to the hostile environment over Iraq,” Squadron Leader Jamie said.

“The first option was to accept refuelling at a reduced speed, lower than normally required, and refuelling at that speed had never been done by me or my crew.

“The other option was to do what we call tobogganing, where we refuel while descending to allow the Hornet to gather more speed. This option would have brought us below a safe altitude, so we went with the first option.”

The Hornet’s pilot was able to coax his fighter into position while the RAAF tanker strove to fly straight and steady at slow speed.

“He did a great job in the end and it was a good feeling to help him out,” Squadron Leader Jamie said.

“If we hadn’t been able to assist, he would certainly have had to make a less than ideal landing in Iraq.”