Zeus is walking perfectly normally. The enormous Ukrainian who has adopted the name of the king of the Greek gods as his nom de guerre doesn't join the others in his team, instead continuing to walk back and forth. For months, they have spent almost every night – frequently under fire – slowly shrinking what is likely the largest minefield in the world, strip by tiny strip. Now, they only have two or three quiet days in their quarters not far from the village of Velyka Novosilka before they are to be relieved by a different unit. They are happy to talk about their mission. But not Zeus.

And there is another thing striking about him as well. His steps make a peculiar sound: "Pffft. Pffft. Pffft." A quiet, pneumatic hiss. The sound of a good prosthesis.

Zeus’s lower right leg and foot is made of metal, plastic and modern technology that, after several months spent at a rehabilitation clinic, allows him to walk completely normally. But he does not wish to talk about the moment half a year ago when an anti-personnel mine detonated underfoot. Others will tell the story later.

Zeus has returned to his specialist unit within the 35th Naval Infantry Brigade for a mission in which any wrong step might be the last.

The primary reason why the Ukrainian offensive has advanced so slowly – more important even than their lack of warplanes and shortage of tanks – are the mines. Sappers like Zeus are arduously doing their best to clear the explosives. And they are not at all surprised by the slowness of the Ukrainian counteroffensive. Indeed, they are instead rather perplexed by the surprise shown by the West.

Sitting on benches and camping chairs beneath the thick canopy of an oak tree, Zeus’s comrades speak of the hell they have gone through over the last three months. Of the anti-tank mines that detonate when a vehicle drives over them, or PARM mines that rip through the sides of tanks, where there is less armor, from just a few meters away. Then there are the buried anti-personnel mines, the trip-wired booby traps and the bounding mines, which spring a few feet into the air before exploding. And small "butterfly mines," which can be dispersed by the thousands from the air.

Taken together, they form an ocean of potential death extending around 1,000 kilometers (621 miles) along the entire front, up to 16 kilometers wide. The men can only advance very slowly, as they are harassed by drones and fired at by distant artillery.

"We frequently come back from missions thinking: Good that we survived that one," says Jaroslav, the 26-year-old commander who has been with the army since 2014. "And a couple of times, after we had finally cleared a section, the Russians dropped cluster bombs on the area. And when we didn’t hear a cascade of explosions, we knew that they were actually new mines."

Sisyphus would be a more fitting name from Greek mythology than Zeus, the name of the figure of legend who determinedly pushed a stone up a mountain only to have it continually roll back down again. Similar to Sisyphus, even though the team is exhausted, they don’t sound discouraged about the fact that they have only made significant progress, a couple of kilometers, in just a few places since the beginning of the offensive in early June.

"It was clear to us from the very beginning, when we received the surveillance photos" of the Surovikin Line in early summer, "that there won’t be a second Kharkiv," says Major Jaroslav, referring to the surprisingly rapid Ukrainian advance near the northeastern city of Kharkiv in September 2022, after breaking through the Russians’ insufficiently fortified lines with lightly armored, fast-moving vehicles. That push was so fast that the Russians fled in panic, leaving behind munitions and hundreds of tanks and other vehicles.

General Sergey Surovikin, Russia’s top commander in Ukraine at the time, learned his lesson. As Germany, the United States, Britain and France spent months vacillating over whether or not to send tanks to Ukraine – a process that Berlin portrays as prudent deliberation – Surovikin rapidly moved to build a defensive line, including tunnels, trenches, bunkers and tank barriers known as "dragon’s teeth." And, especially, minefields.

"They have always been extremely good at laying mines," says Oleksandr, Jaroslav’s deputy. "They shouldn’t be underestimated. They quickly learned from their mistakes."

Many in the West had anticipated that the long-awaited Ukrainian spring offensive would rapidly push the Russians back. The hope was that Leopard 2 tanks from Germany, Bradley fighting vehicles from the U.S. and Ukrainian troops trained in the U.S. and Europe would be able to advance far enough that the Russians would no longer be able to supply their troops.

But when the modernized units headed out in early June, they didn’t get very far. Vehicles would be struck by Russian artillery or rockets. Others would deviate from the tracks of those in front of it at night and roll onto a mine.

The wounded had to be tended to, with medics jumping out of vehicles and taking cover in shell craters, which were also mined. Suddenly, more casualties had to be tended to and the stationary vehicles made for easy targets. Evasive efforts frequently set off yet more explosions. Losses of materiel – and, more importantly, personnel – were high. The big offensive thrusts were stopped.

"It was awful," says Yuri, a surgeon from Odessa who works in a regional hospital not far from the front. He scrolls through his phone, showing photos of the injured who were brought in – and explaining what the bloody images full of bone chips and tissue depict. "This here is a hand. That is a leg that was missing 15 centimeters of the shinbone. What kind of war is it where you don’t even see your enemy? We only get blast victims. I haven’t seen anyone with a gunshot wound since June."

In order to strike the large, visible and sometimes immobile Ukrainian vehicles, the Russian military improved its arsenal. It now has a variety of different drones, including the feared Lancets, and Moscow is also relying on the helicopter gunship Alligator, which can fire guided missiles from a greater distance than can be reached by Ukrainian anti-aircraft defenses.

Most of all, though, say Ukrainian officers from a number of different units, the Russians have focused their attentions on those hulking machines designed to clear minefields quickly and safely – such as the Soviet-era UR-77 Meteorit or the German-supplied mine-clearing vehicle Wisent 1.

The military leadership does not want journalists to get near such equipment for fear of divulging their location. As such, it was only a chance stop on the side of the road that led DER SPIEGEL to a Meteorit unit. "The entire army only has 10 of them left," says a soldier. And several of them are right here, parked beneath the thick canopy of a small forest. The decades-old giants fire off lines to which clusters of small explosives are attached, designed to detonate all mines within an area measuring 90 by six meters.

The soldier laughs, saying that Meteorit might be a fitting name for the vehicle itself, but not for the team that operates it. "The armor is only two to eight millimeters thick. It should never go into battle. We call ourselves the molecular kitchen." A single strike at the wrong moment, he says, and not much will be left of the crew.

"The Wisent mine-clearing tanks, though, are great," says Oleksandr, and begins listing off the amenities. "Night-vision, automatic transmission and a modular construction so that broken parts can be quickly replaced." It is a huge advantage when you come under fire in the middle of a minefield.

"But these systems unfortunately have one decisive disadvantage," he continues. "They are big, slow and easily recognizable." The Russians, he says, are constantly on the lookout for them.

Which is why the mine-clearance teams often leave them parked and head out with a combination of highly modern technology and superannuated methods. To determine whether mines are hidden in a certain area, camera drones equipped with infrared sensors are first deployed, usually at around 2 or 3 a.m. Anti-tank mines in particular store daytime heat longer than the surrounding earth, and the old TM-62s are especially easy to spot using the method.

Once they have been identified, the men head out in small groups, usually with a metal detector – "but they are useless if there is too much shrapnel in the ground," Oleksandr admits. In such cases, they turn to a device that doesn’t have much in common with the high-tech equipment otherwise used in this war: a metal rod that is shoved diagonally into the ground.

It's an extremely slow process. Too slow, believe some U.S. military officers, who have turned to the media to anonymously criticize the Ukrainians of hesitance. It is a sensitive issue, despite the Ukrainian gratitude for U.S. weapons deliveries. Major Jaroslav recalls a piece of advice comrades received from a U.S. general: "If you’re not making progress through a minefield, he advised calling in air support or going around the obstacle."

Standard practice, to be sure, "but we don’t yet have any modern F-16s, and how are we supposed to go around this?" Jaroslav demands, his voice raised for the only time in two days. "The Russians have mined the entire front, 1,000 kilometers long, and as we are busy clearing them up here, they are laying new ones, a fourth and fifth line. They’ll keep going like that until the Sea of Azov. How are we supposed to get around that!?"

The reality of Velyka Novosilka and the tiny steps being made by the 35th Brigade have brought the lofty expectations of Western military leaders and politicians back down to earth. Or perhaps even a couple of centimeters below that.

"Grass!" says Jaroslav, in a tone of voice that makes it seem as though evil incarnate is hiding among the clumps. "When it’s half a meter tall or taller, like it is now, we can no longer tell what may have been buried there a few months ago." The images from the infrared cameras of the drones are also blurry if there is too much vegetation growing over the mines.

Late summer meadows are the stuff of nightmares for the team of sappers. But the men say they are looking forward to late fall – the season that military strategists warn of. When the rain starts falling, the ground turns into a sticky sea of mud that can even ensnare battle tanks. But for mine clearance units, November is a paradise: "No plants to cover up the traces, no leaves in the trees to block visibility."

In the depths of winter, though, Jaroslav continues, it is again impossible to read the ground. "Snow is bad. Fresh snowfall is hell." After just half an hour, it covers everything so uniformly, he says, that their only option is to use probe rods – which also don’t work in frigid temperatures when the ground is frozen.

One of the biggest questions currently hanging over the Ukrainian offensive, is whether it will fail because the troops aren’t advancing quickly enough and have only "about 30 to 45 days’ worth of fighting weather left," as Chairman of the U.S. Joint Chiefs of Staff Mark Milley told the BBC recently with an eye on the approaching autumn. That question, though, says Jaroslav, is the wrong one.

After all, what good is hard summer ground on which the new Leopard and Bradley tanks can race forward if they get stuck in the middle of a Russian minefield and are shot to bits? On the other hand, Major Jaroslav says, nothing is lost if it takes a bit longer. Plus, they are moving forward – 50 meters on some days, 100 on others. The night before, he says, infantry units managed to liberate the village of Robotyne, around 10 kilometers behind the June line. Another 10 kilometers or so from there and the highways and rail lines used to supply the Russians will be within range of American rocket launchers.

We head out in an unarmored minibus together with Jaroslav and his team from the 35th Brigade to an area slightly removed from the battlefield. The mission: disarming a potential mine. The bus drives through villages that have been almost completely abandoned, almost every single house showing damage. It is also striking that there are no sunflowers. In normal times, they are everywhere in late-summer southern Ukraine, two meters tall as fall approaches, their heavy heads swaying in the wind. But not here. Nobody dared plant the fields, which are now full of the high grass that everybody fears.

The men find the spot where a small detonator is sticking up out of the ground behind a large warning sign. But it’s just a dummy, with no explosive charge, put there by a different Ukrainian unit that wanted to keep people from passing through, but failed to tell anybody that it was a fake.