Russian troops are trying to drag Radkivka, a village on the northern edge of Kupiansk in Kharkiv Oblast, into the gray zone so their infiltration groups can keep reaching the city, Viktor Trehubov, spokesperson for Ukraine’s Joint Forces Grouping, said on national television on 27 October, Ukrinform reported. Russian forces made three attempts to advance toward Radkivka on 26 October, Ukraine’s General Staff reported.

Russia has tried for more than a year to retake Kupiansk, a city on the Oskil River, largely by slipping small groups through a disused gas pipeline under the river. They kept using it even after Ukraine said in September 2025 that it had flooded three of the four pipe strings, until Ukrainian troops went into the pipes themselves in Operation Veles, announced on 22 October.

Russian groups now have to move above ground

The pipe Russian groups used to seep toward Kupiansk has been put out of action, so they now have to go through Radkivka or neighboring Holubivka, Trehubov said. They move along the bank of the Oskil and a nearby tree line, but the foliage will soon be gone, which will make that much harder.

On the western bank of the Oskil, Russian forces took losses from Ukraine’s Khartiia Corps and in Operation Veles, and their logistics have “suffered noticeably,” Trehubov said. Advancing there is now harder for them than it was a month ago, he added.

Everything now depends on how the fights for Holubivka and Radkivka end, Trehubov said.

“If Ukrainian control can finally be established there, the Russians will have nowhere much to crawl through,” he said.

Several dozen Russian soldiers remain in low-rise buildings in northern Kupiansk, and Ukrainian forces are working to cut off their rotations, Trehubov said on 23 October.

Each side wants the other off its bank of the Oskil

On the eastern bank, Russian forces keep pushing toward the village of Podoly and Kupiansk-Vuzlovyi, a railway junction town southeast of Kupiansk, aiming to wipe out Ukraine’s foothold there, Trehubov said. Ukraine wants to destroy the Russian foothold on the western bank.

“For that, we will need to at least somehow throw them out of Dvorichna,” Trehubov said, referring to a town north of Kupiansk.

The US-based Institute for the Study of War (ISW) assessed that Russian forces conducted no offensive operations on the Kupiansk axis on 26 October, likely because Ukraine now controls the pipeline, a view at odds with the General Staff’s report for that day.

Ukraine reported confident control of Kupiansk as early as February, yet Russian groups kept slipping into the city for months afterward. Trehubov’s latest assessment stops short of declaring that threat over: Russia will still try to advance, he said.

Ukraine's Defense Forces advanced more than 15 km through underground utility tunnels into Russia's rear on the Kupiansk axis in Kharkiv Oblast, the Khartiia Corps of Ukraine's National Guard reported on 22 October. The corps called it Operation Veles. The underground advance was paired with attacks on the surface and drone strikes, hitting Russian forces from two directions, the corps told Militarnyi.

Russian troops have repeatedly crawled through gas pipelines around Kupiansk to get behind Ukrainian lines, even after Ukraine reported confident control of the city in February. This time, Ukraine went underground itself. The operation took away Russia's chance to get into Kupiansk's rear, the corps said.

The corps reported more than 30 Russian soldiers captured and Russian losses of more than 100. Militarnyi, citing the unit, put the number of Russian troops killed at over 100.

Khartiia studied how Russian troops moved through pipes before going underground itself, the corps commander, Brigadier General Ihor Obolenskyi, said.

"We watched how the enemy works underground and studied how they do it. The Russians intended to use gas pipelines to get into the rear of our troops. So we went underground ourselves. We anticipated the enemy's actions and mastered the tactics of underground combat," he said.

For the operation, troops trained physically and psychologically to fight in confined spaces, sappers and engineers prepared the underground route, and special communications, navigation, silent logistics, and life-support systems were put in place, Khartiia told Militarnyi. The operation was named after Veles, the Slavic pagan god of the underworld.

Khartiia's brigade, the R.U.H. assault regiment, the Lava drone regiment, the Achilles drone brigade, and units of Ukraine's military intelligence, including the Freedom of Russia Legion and the Russian Volunteer Corps, took part, the corps said.

Russia has used pipelines to infiltrate before

By September 2025, Russian forces had used pipelines to move troops behind Ukrainian lines three times, Ukrainian monitoring project DeepState reported on 12 September 2025. The first was in Avdiivka, the second near Sudzha, and the third near Kupiansk, where groups crossed the Oskil River through a gas pipe.

Near Sudzha in March 2025, Russian special forces walked through a pipeline that until recently had carried Russian gas to Europe, the Associated Press reported. A pro-Kremlin blogger claimed they covered about 15 km and that some spent several days inside.

Russian troops kept using the pipeline near Kupiansk this year. On 27 September, Khartiia's reconnaissance drones recorded Russian forces leading nine civilians, including children, elderly people, and a person on crutches, through the gas pipeline out of the Kupiansk community. Men of military age in civilian clothes walked alongside them, and the corps believes they were Russian soldiers using the group as cover to withdraw. Ukrainian troops held fire because of the civilians, the corps said, adding that the case has been documented for a war crimes investigation.

Why the war is moving underground

Drones, constant surveillance, and AI-assisted targeting have made the battlefield surface transparent and deadly, argue John Spencer, chair of urban warfare studies at West Point's Modern War Institute, and Col. Drew Craig, principal military engineering staff officer at NATO's Allied Rapid Reaction Corps. In an August analysis, they write that soldiers in Ukraine describe a "death zone" of some 30 km, where moving above ground can draw an attack within minutes. When firepower makes the surface too dangerous, armies have historically gone underground, as they did in World War I and Vietnam, and more recently in Gaza and Lebanon.

"Armies that cannot survive above ground must adapt below it," the authors write.

Fighting in tunnels brings its own requirements, the authors write: detecting the enemy by sound and vibration, and specialized unmanned systems that cannot rely on GPS or stable radio links. Long stretches underground also take a severe psychological and physical toll on soldiers.

Western militaries are not ready for this, Spencer and Craig write. No NATO partner maintains even general capabilities for large-scale underground warfare, and US and British efforts focused mainly on detecting and clearing tunnels rather than occupying and operating in them.