Large, fixed-wing drones, known technically as medium-altitude, long-endurance (MALE) drones, were common in the US-led wars in Iraq and Afghanistan, where unmanned aircraft such as the Reaper were used to hunt down insurgents and terrorists.
The drones were often operated from about 12,000km away at the Creech Air Force Base in Nevada.
There is now evidence the hunter has become the hunted.
Since October, the US may have lost about four $30 million Reaper drones in attacks by the Houthi rebels in Yemen and Iran-backed militias in Iraq.
Israel has also lost at least four of its Hermes drones to Iran-backed Hezbollah in Lebanon, while Turkey has lost at least one Anka drone to Kurdish militants.
Around one thousand of this type of drone remain in service around the world, partly due to their ability to remain airborne for hours.
They are distinct from one-way attack drones, quadcopters and smaller reconnaissance drones, which sometimes resemble remote-controlled hobby planes.
Detractors say MALE drones increase the risk of civilian casualties because operators and commanders become detached from battlefields due the remote nature of the fight.
The drone strike that killed 10 civilians during the evacuation from Kabul in 2021 is one example used by critics of the drone.
But in crises including the Nagorno-Karabakh conflict, Libya's civil war and a Turkey-Syria clash in 2020, the use of the drones was credited with turning the tide of battle.
Drone survival
Analysts have long warned that, while MALE drones can be effective in conflicts such as Afghanistan and Iraq, they might not last in a full-scale war.
"Predators and Reapers are useless in a contested environment," former US general Mike Hostage said in 2013.
That became apparent in Ukraine, where Kyiv’s early success with Turkish Bayraktar TB2 drones, which were used to blunt a Russian offensive on the capital, soon faded as the Russian military adapted its tactics.
The drones’ slowness and relatively large radar cross-section was a notable vulnerability, restricting them to low altitudes where they became the targets of short-range missiles and guns.
Once Russia adapted, Ukraine lost at least 24 of the aircraft, each costing $5 million.
The Houthis, Hezbollah in Lebanon and Iran-backed Iraqi militias including Kataib Hezbollah are not as well armed as Russia, but they still possess rudimentary air defences and long-range missiles that can be used against drones.
In April, the Houthis shot down a Reaper over Yemen. It came after a Reaper was shot down in January in northern Iraq, with US officials saying the weapon used in the attack was probably provided by Iran.
It is believed to have been a 358 loitering munition.
The 358, which can reach altitudes of about 25,000 feet, flies in a figure-eight pattern until its sensors detect an enemy drone. Various reports suggest two Israeli Hermes 900s have been lost to the 358.
The militias have celebrated the destruction of each drone on social media, but is it really such a victory?
Fighter jets versus drones
At $30 million, a Reaper drone is still less than half the cost of the most advanced F-16 jet, the Block 70/72.
Unmanned drones eliminate the risk of losing a pilot, whose training can cost more than $10 million.
Jets including the F-16, the F-18 Super Hornet and the F-15 are equipped with increasingly advanced “targeting pods”, such as the sniper pod, which can track troops and vehicles at high altitudes, traditionally a capability of drones.
But drones aren't just cheaper to build. F-16s can cost anywhere from $8,000 to $27,000 an hour to operate.
The operating cost can increase to more than $40,000 an hour for more advanced jets including the F-35.
The cost of operating a Reaper is estimated to be $3,500 an hour.
Meanwhile, Reaper maker General Atomics says its airframe has a 40,000-hour lifespan, compared with the F-16's 12,000 hours.
Shooting down a drone can be deemed a success by militant groups "as it reflects their ability to counter western air assets", said Sam Cranny-Evans, a research fellow at the UK Royal United Services Institute think tank.
“Although relatively slow and readily detectable – which makes them an easier target to shoot down in air defence terms – MQ-9s [Reapers] and others have evaded most non-state actors for over 20 years and enabled the West to have persistent uninterrupted surveillance and target acquisition, if they chose to do so."
“In that sense, shooting one down degrades ISR [intelligence, surveillance and reconnaissance] capabilities for a time and imposes costs on the observer that are not insurmountable, but may change behaviour if they continue.”
The ISR capabilities of drones are significant. Reapers can carry ground moving target indicator-enabled radar that can track vehicles and people when if there is clouds or fog and they can be used at night.
Reapers can also be equipped with an array of nine large cameras, known as the Gorgon Stare, that can monitor activity in villages or towns. Israel’s Hermes drones have a similar capability called SkyEye.
Mr Cranny-Evans points out that the Houthis, during the height of Yemen's civil war, successfully shot down enemy jet fighters and helicopters.
“For the Houthis, this is sort of par for the course. They have experience of downing advanced aircraft and don’t shy away from doing it.
"Hezbollah also has past form in this regard, but have less success against fast jets. If those capabilities have spread to actors that previously didn’t have them, then that’s problematic, but it has been anticipated for some time.”
Adapting drone strategy
Experts say countries including the US, Israel and Turkey will continue to use fixed-wing drones for the foreseeable future, but have not ruled out a change in tactics.
Drones can be fitted with alert systems to detect missiles, while magnesium flares can be added as a defence mechanism, but this adds cost and weight, potentially reducing the time they can remain in the sky.
Even so, drones are likely to remain significantly cheaper than manned aircraft.
“I think the limitations on where large expensive drones can operate without being shot down were bound to increase over time,” says Sophy Antrobus, an expert on drones at the Freeman Air and Space Institute in London.
She says militaries are changing how they evaluate the systems, rather than viewing them as potentially obsolete.
“The RAF recently published a new drone strategy which discusses these challenges," she says. "In short, drones such as the Reaper are seen as high value and kept out of harm’s way as much as possible, while more disposable systems [are developed] that we are prepared to lose.”
Mr Cranny-Evans agrees with that assessment.
“For those forces with relatively advanced capabilities, shooting drones down is probably expected." he says. "For those that previously did not have them, it’s an unwelcome development for western countries that might want to maintain a lower cost threshold, but it’s not unexpected.”
Unwelcome, perhaps, but not necessarily dangerous enough to put victory in war at risk.
The US lost dozens of drones to accidents in Afghanistan and Iraq, but has doubled down on MALE systems. The US Marine Corps recently increased its Reaper orders.
But there are concerns the technology on drones could fall into the wrong hands when drones are shot down. Iran has based several of its drone models on captured US equipment.
“One would hope or expect that the software that makes these systems work is encrypted and has the ability to be remotely wiped,” Mr Cranny-Evans says. "If that is the case, it would make useful technical exploitation quite difficult."
