Since December, the Russian army has been building large fortifications all along the front line. Satellite imagery shows that its troops, which invaded Ukraine in February 2022, are digging in at strategic points in the occupied territories and preparing for a counteroffensive. According to British intelligence, no installations this big have been constructed anywhere in the world for decades.

After analyzing thousands of new satellite images, the Reuters news agency also reports that new bulwarks have appeared in the Russian border regions, as well as in southern and eastern Ukraine: trenches, roadblocks, and ditches stretching for hundreds of kilometers (miles).

Rob Lee, a senior fellow at the Foreign Policy Research Institute in Philadelphia, believes Russia has learned from Ukraine's successful counteroffensive last year. "After the Kharkiv offensive, Russia kind of realized that defeat was possible — they could lose territory. I think that was a realization that Ukraine can do offensive operations," he told Reuters.

What bulwarks are the Russians building?

The fortifications primarily consist of trenches, deep enough for a person to stand in. They are reinforced in front with sandbags or rocks to protect the Russian infantry from bullets, shrapnel and artillery fire.

Brady Africk, an analyst at the American Enterprise Institute in Washington who has examined the satellite images, says there are now many emplacements like these along key roads and outside strategic cities.

According to Reuters, the images also show that the Russians aim to block the path of Ukrainian heavy equipment using various obstacles such as Czech hedgehogs, anti-tank ditches, and concrete blocks similar to the "dragon's teeth" deployed during World War Two. Observers report that the Russians are also laying mines.

Where will Ukraine attack?

The places where Russian military command is constructing the biggest fortifications are clearly where it thinks Ukraine is most likely to attack. Accordingly, Russian front-line positions are concentrated in the southeastern part of the Zaporizhzhia region, in eastern Ukraine, and around the isthmus connecting annexed Crimea with the rest of Ukraine.

Mick Ryan, a retired major general in the Australian Army, notes that the Russian military clearly suspects southern Ukraine in particular, and especially the region around Zaporizhzhia, will be the focus of a Ukrainian counteroffensive.

"These are serious fortifications, constructed in the space of six months," says Oleh Zhdanov, a Ukrainian military expert and colonel in the reserves. However, he stresses that the installations are dotted about piecemeal, and that the road network east of Melitopol, for example, is hardly blocked at all.

Mitigating Russian weaknesses

Niklas Masuhr of the Center for Security Studies at ETH Zurich suspects that the Russians have built these fortifications not so much to try to keep Ukrainian forces out along the whole of the front line but rather as a delaying tactic, and to "make Ukraine pay more in lives and time" during the counteroffensive. "The fortifications add a degree of predictability and structure to future operations," Masuhr explains. "This mitigates Russian weaknesses, since [the Ukrainian Armed Forces] tend to be better at improvisation and fluid military situations." However, he also comments that tying the Russian forces to the fortified areas means they also become more predictable, as their positions can be identified in advance. 

Rob Lee from the Foreign Policy Research Institute notes that concentrating their own troops on a specific section could give the Ukrainians an advantage and allow them to push deep into Russian-occupied territory. This in turn could destroy other lines of fortifications and lead to a bigger breakthrough, he says.

Ukrainian air defense and Russian fighting morale

The satellite images do not show the artillery positions yet, however, Oleg Zhdanov warns, because the Russians only show up just before the fighting begins. Russian aircraft are also an important factor, says Zhdanov. However, he adds, thanks to Ukraine's air defense, they rarely penetrate Kyiv-controlled airspace.

"What is important is that the attacking Ukrainian forces have enough tactical air defense systems to directly protect the troops," he says, adding they will be followed by air defenses at the operational-tactical level that cover complete areas — "a very serious factor that needs to be taken into account."

However, the outcome of the counteroffensive does not depend solely on the Russian fortifications in the occupied parts of Ukraine, though observers argue they may very well obstruct a major Ukrainian army breakthrough. "No matter how you dig in or fortify, the most important moment in defense depends on the soldier's will to defend and on his emotional and psychological state," according to Zhdanov, who recalls that during the occupation of Kherson, the Russian military built fortifications three lines deep along the city limits for almost half a year. The Ukrainian army liberated the city nevertheless, he says.

Traditional fortifications and modern warfare

The Ukrainian goal must be to "set off paralysis in the Russian military leadership and panic across the Russian rank and file," says Franz-Stefan Gady, a specialist in modern warfare and analyst at the London-based Institute for International Strategic Studies. "Intangible factors such as tactical surprise, battlefield leadership and fighting morale will likely be decisive in the first 24 hours of an attack," he told CNN.

Offensives in modern warfare tend to be carried out by small, highly maneuverable groups, says Zhdanov, pointing out that in Ukraine's liberation of the Kharkiv region, extremely mobile units broke through the gaps between fortifications and trenches but did not engage in combat. "They create chaos and panic among the enemy, and the main troops conclude the attack," the expert says.

The significance of Western military aid

"Tanks and other armored vehicles must operate alongside engineers, artillery and even aircraft to defeat layered defenses — an approach called 'combined arms,'" says Rob Lee from the Foreign Policy Research Institute. Recent shipments of Western military gear are designed to aid the effort, he says.

Oleg Zhdanov says Ukraine has received mine-clearing tanks, but he also points out in particular American M58 MICLIC mine-clearing equipment, as well as Biber armored bridgelayers for overcoming small obstacles and Badger armored engineering vehicles, both provided by Germany.

Western support will also be key in promoting the Ukrainian armed forces' ability to operate in combined arms groups and allow effective cooperation between different units in combat, according to Niklas Masuhr. The equipment and ammunition along with continuous intelligence support are crucial, the expert says.

Smart planning might be even more critical than Western arms, says retired Australian Major General Mick Ryan. "The most important assistance they have received is not so much the equipment, but the training of battalion and brigade and higher-level staff in these very complex combined arms activities," he says. "You can't just get a pickup team and do this. It is the most complex ground operation you can conduct."

"We've really never seen ZSU [Armed Forces of Ukraine] assaults against entrenched Russian positions at anything close to this scope during the war. Previous counteroffensives were conducted against weakened, spread-out Russian forces," says Niklas Masuhr from the Center for Security Studies at ETH Zurich. "This is a new setting."

This article was originally written in Russian.