Tehran purchased six of the twin-engine RH-53Ds from Sikorsky before the 1979 revolution. But the complex machines—which can carry troops and supplies and also drag water-skimming minesweeping sleds—quickly fell into disrepair after most of the world imposed sanctions.

Lucky for Iran, in April 1980, U.S. Special Operations Forces left behind five intact RH-53Ds during their abortive—and, for some, fatal—attempt to rescue American hostages in Tehran.

Engineers at Iran’s state aviation enterprises pillaged the abandoned RH-53Ds for parts and brought the original six copters back to working condition—for a few years.

But by 1988, just one RH-53D was flightworthy. Tehran began acquiring spare parts illicitly from American and Singaporean agents working on Iran’s behalf.

In recent years, the Iranians not only restored the six original RH-53Ds—they also had enough parts left over to repair one of the copters the Americans had abandoned.

That boosted Tehran’s RH-53D fleet to seven machines. Based on their participation in certain war games—including the January naval exercise where “704” debuted its new refueling gear—the boxy copters apparently spend much of their time transporting Iranian commandos.

An RH-53D on internal fuel can travel more than 600 miles with a modest load. With aerial refueling, it could cover much, much more ground—flying until its lubricants ran low and its crew wore out. With inflight refueling, Iran’s RH-53Ds could carry out commando raids across the Middle East.

The U.S. military long ago fitted refueling probes to its own H-53 helicopters. But the Americans also bought special KC-130 prop-driven tanker planes that can fly slow enough—around 150 miles per hour—to allow the copters to plug their probes into the hoses the tankers trail behind them.

Iran has C-130s, but has not copped to modifying any of them for inflight refueling. Instead, Tehran continues to rely on two Boeing 707 tankers and the world’s only 747-based tanker. It’s unlikely either of the Boeing jet models could safely fly slow enough to refuel a helicopter.

And that means one of two things. One—Tehran added a refueling probe to an RH-53D for experimental or even propaganda purposes and does not intend to deploy it operationally. Or two—Iran is also working on a new tanker.