ANALYSIS: Digging Trenches – Ukrainian Military Engineers and the Art of Preparing Field Defenses

The common view is that the supply of weapons and other military aid to Ukraine is the fundamental key to countering Russian aggression, but the creation of strong defensive positions and all that goes with that is proving equally vital.

As former British Army General Sir Richard Barrons wrote in an article called “Dig or Die – Trench Warfare in the 21st Century” in February 2023: “A hole in the ground is as fundamentally important to success or failure, life or death, in war today, as it has been for hundreds of years.”

This is amply demonstrated by the way Russia’s extensive Surovikin three-deep lines of defense, which consisted of minefields, dragon’s teeth, wire and fortifications resisted much of Kyiv’s 2023 counteroffensives. It was not, however, the fortifications alone that resisted Ukrainian forces but the combination of them and the mass artillery that supported them.

Such construction is proving just as crucial as Ukraine’s forces face Moscow’s attempts to breakthrough in the Kharkiv region and other sectors of the front line.

Some call for Ukraine to create a modern-day version of France's Maginot Line in its border areas – a line of concrete fortifications, obstacles and weapon installations such as that built by France in the 1930s to deter invasion from Germany, in the belief this will stop Putin’s hordes.

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No matter how good the protection fortifications offer they are just as susceptible to failure by being destroyed, bypassed or overrun, unless other elements of dynamic defense are in place to protect, support and exploit the resistance it offers to enemy forces.

An article in Politico in March said that Ukraine’s preparations of new defensive lines were “too little, too late,” despite the allocation of more than $800 million for that purpose in February. Concerns voiced at the time included a shortage of landmines for barrier construction and fears that what had or was being built was insufficient to resist the Russian use of aerial glide bombs and massive artillery barrages.

Others complained that the defenses were being constructed too far back from the Ukrainian-Russian border, thereby effectively ceding more occupied territory with videos posted on social networks apparently showing Russian infantrymen crossing the border and advancing unhindered.

The reality is that Ukraine had to construct its new defensive lines under constant threat of artillery, missile and ground forces attack. For that it needed to be out of range of the most destructive Russian weapons for as long as possible to ensure the barricades and strong points it needs could be finalized.

The US Army’s Field manual FM 5-15, entitled “Field Fortifications,” was first published in the 1940s and runs to almost 300 pages. It details the rationale behind the need to build trenches, weapons emplacements, overhead protection and goes into great detail on preparing, siting, and building the position including advice on which materials to use. Despite being more than 80 years old many of the principles it espouses are still relevant today.

It was superseded by two separate manuals, FM 5-102 which addresses “Counter Mobility” [obstacles] and FM 5-103 “Survivability” [protection]. These manuals that were first published in the 1980s are much more concerned with planning considerations rather than on the nuts and bolts of building field fortifications.

The purpose of defensive positions

In planning and executing a defensive line the tenets of all three of the above documents need to be considered – and that is what is being learned and put into practice by Ukraine’s military engineers as they prepare for the anticipated next Russian offensive.

It must be remembered that the fortification is not an end to itself, it must be part of a wider strategy aimed at defeating the enemy. A good defensive position is not only intended to stop an enemy attack but it to give the defenders time to mount their own offensive operations to destroy or at least push the enemy back. The defensive plan should contain four interdependent elements:

• Preparation, planning, siting and construction of the defensive position.
• An obstacle plan supported by covering fire to disrupt and channel the enemy into “killing zones.”
• Concentration and siting of reserve forces, direct and indirect fire support.
• Flexibility and “what if” options within the overall defensive plan.

Military engineers must work with the commander and his staff to choose the ground they wish to defend and to understand how they want to set the conditions for battle. Engineer functions and forces are a critical component in setting the conditions for combat and giving the defenders the edge against the attacker.

The military engineer must understand the enemy’s capabilities, weapons and tactics as well as the commander’s plan along with the strength, weapons and ability of his own forces before planning and constructing his lines of defense. He combines this with his understanding of the topography to select the best defensive position which can combine with and complement the fortifications that the engineers build.

In an all-arms battlefield, such as the war in Ukraine has become, the main threats are from aircraft-delivered bombs or missiles, field artillery, tanks, and other armored vehicles with dismounted infantry being last but by no means least.

Indirect artillery fire presents the main threat on Ukraine’s battlefield with some estimates indicating that it is responsible for almost two thirds of casualties received on both sides. The defensive position must be able to protect its occupants from the effects of direct impacts from high explosive ammunition, as well as above ground air bursts and cluster munitions.

This means that there is an absolute requirement for overhead protection. Gen. Barrons says this should be a minimum of one meter (3 feet) thickness of compacted earth or sandbags while recommending “much, much deeper so that people can eat sleep and survive immune to the effects of the pounding at ground level.”

The military engineer then has to consider what materials are needed to maximize the levels of protection. The obvious answer is concrete but in the era of modern weapons the material itself can become a major hazard as splinters and shards of concrete are thrown off by attack. For that reason, wood is extensively used in building the position – it is strong, offers a much less secondary hazard and, especially in Ukraine is readily available.

In the pre-satellite and aerial drone days camouflage was an important factor in establishing the defensive position. In 2024 Russia was able to observe the building and location of every centimeter of construction as Ukraine had been able to spy on the Surovikin line. Far more critical is the use of screens and camouflage netting to obscure activity in the position from visual observation and directed attack such as that which can be inflicted by first person view (FPV) drones. This must be continually repaired and replaced as military action can degrade its effectiveness.

A typical main line of defense is illustrated below.

The first line of defense is generally a combined minefield and barbed-wire entanglements which, to be most effective, should be covered by both direct and indirect fire to prevent the enemy from clearing a way through at his leisure.

Next come obstacles designed specifically to impede the progress of armored vehicles – dragon’s teeth and anti-tank ditches – which again should be covered by fire. A tank negotiating a line of concrete blocks, or a ditch often exposes its vulnerable underbelly to attack.

Behind the obstacles is the main trench, which for defensive positions intended for medium to long term occupation may include semi-permanent structures such as pillboxes, trenches, dugouts, sleeping, living and cooking areas, more direct fire weapon or mortar positions.

Defensive lines can be replicated and repeated to provide even greater in-depth protection. Russia’s Surovikin line in eastern Ukraine had three or more lines of defense through which attacking forces needed to negotiate before achieving a breakthrough.

The defense line must be supported by artillery to provide fire support to disrupt enemy assaults or to deny areas to the enemy and to divert them into “killing grounds” of the defender’s choosing. Along with artillery positions, it is also important that there are sufficient reserves of men and equipment retained beyond the line of defense. The reserve should be able to reinforce areas where the enemy may be threatening a breakthrough or to initiate counterattacks against enemy forces.

In putting together its defensive positions, the Ukrainian military engineer considers all of these aspects discussed here. Judging by the ability of Kyiv’s forces to resist the current Russian offensive around Kharkiv, despite Moscow’s numerical superiority in troop numbers and artillery, they have done a pretty good job.