FROM tiny quadcopters buzzing over frontline trenches with cameras and grenades to flying bombs lugging warheads weighing dozens of kilogrammes into Kyiv and Moscow, drones have marked the Ukraine war like none before it.
In recent months, invading Russian troops have sent waves of Iranian-made Shahed explosive drones at Kyiv and other cities, while Ukraine has launch-ed unmanned attacks of its own in Crimea and the Russian border region Belgorod.
The Russian government even accused Ukraine on Tuesday of attacking Moscow with such devices.
This is a far cry from the hype surrounding Turkish-made Bay-raktar TB2 drones in the early months of the war.
The aircraft made headlines and were praised for their role in smashing Moscow's armoured columns and the Black Sea fleet flagship, Moskva.
But such models — known as Male, for medium altitude, long endurance — have lost relevance as the conflict has dragged on.
"The front has stabilised and become impenetrable, as the Russians have deployed systems" to defend against attacks from the air, a European defence industry source told AFP on condition of anonymity.
Now the drone war has become a numbers game. Most self-detonating drones are downed by air defences, "used to force defenders to fire their missiles and run down reserves", a senior French military source said.
"You also create terror and uncertainty at all times. Over the long term, that has value."
Eroding enemy air defence cheaply is vital for Russia, whose production of long-range missiles is limited to around 40 per month, analysts Jack Watling and Nick Reynolds of British defence think tank Rusi wrote in a recent report.
Moscow's air force "launches large numbers of aircraft to increase the number of potential axes of threat... (and) to identify gaps in Ukrainian air defence" where traditional missiles could get through, they said.
Kyiv also uses "commercially available Chinese propeller-powered drones or old Soviet jet-powered reconnaissance drones" that can attack "well inside Russian territory", the European industrial source said.
The vast majority of drones are smaller models used on the front lines for reconnaissance and attack.
Ukrainian troops have published many videos on social media showing modified commercially available drones dropping bombs on Russian soldiers' positions.
On any given 10km stretch of the frontline, "there are between 25 and 50 UAVs (unmanned aerial vehicles) from both sides", Rusi's Watling and Reynolds wrote.
Purpose-built Ukrainian Furia and Russian Eleron-3 drones have a range of 50km, while modified commercial quadcopters, many bought through crowdfunding, can venture fewer than 10km.
The swarms have pushed both sides into deploying electronic defences, lowering the cost of countering devices that are too cheap to be worth shooting down with pricey missiles.
Russian forces "now employ about one major electronic warfare system per 10km of front-age", said Rusi, with "more specialised EW capabilities" further up the chain of command.
"The Russians have stepped up their electronic warfare game. It's a huge change," the senior French officer said.
Even Russian platoons are now equipped with anti-drone weap-ons, Rusi said, including directional jammers and arrays for hijacking UAVs.
Anti-drone rifles that emit jamming signals are "the absolute basics of defence. What works are non-portable jammers deployed close to the frontline", the European industry source said.
But such "big spheres on tripods with generators" are "easily spotted and have a limited life expectancy", they added.
With so much energy going into their destruction, most small drones "won't fly more than four or six times before being shot down", the officer added.
Ukraine has said it is losing around 10,000 drones per month across the large range of devices it uses, a figure impossible to verify.
Ukraine could use drones to clear Russian defensive barriers in its expected summer attack, for instance, "to drop explosives on a minefield, blowing a path through", Vikram Mittal, a professor at US military academy West Point, wrote in Forbes.
The writer is from the Agence France-Presse news agency