Russian troops have completely withdrawn from their bridgehead across the Dnipro river in Kherson oblast, which includes the cession of Kherson city and the effective demolition of the Antonovsky bridge. 

General Sergei Shoigu, Russia's defence minister, issued the withdrawal order even though Ukrainian army units had made no progress towards Kherson beyond the 30-km advance to Dudchany last month. They are now simply occupying vacated space.

This begs the questions why? And why now?

The questions surrounding the withdrawal are set within a larger and earlier unanswered question, namely what was Moscow’s original objective on February 24, and why did it take the Kherson bridgehead in the first place? In truth we don’t know the answer, but it seems more than likely that Russia’s objectives included taking Ukraine’s whole Black Sea coast down to Odesa. The only way to do that was to secure a large bridgehead on the Dnipro's west bank to provide a base area from which to build force for a later 200-km strike west to the borders of Transnistria.

The first part of the plan – advance 150 km from Crimea to Kherson and establish a contact line a comfortable distance west and north of the river – met no effective opposition. Russian forces swept into and past Kherson in the first week of the war with hardly a shot being fired. It is possible that Moscow expected other parts of its invasion of Ukraine to meet with as much success.

Unlike its neighbouring oblasts across the river, the majority of Kherson’s population is of Ukrainian ethnicity. In Kherson, Russia was more of an invader than a liberator. However, Moscow kept hold of Kherson, tying down ten identifiable Armed Forces of Ukraine (AFU) brigades (almost of a quarter of Ukraine’s ground forces) at first in a defence posture and latterly in a largely unsuccessful counter-attack.

Defence trumps attack

What we do have, though, is a growing understanding of the nature of modern ground warfare, which clearly reveals that the balance between “defence” and “attack” is today firmly in favour of defence. If an advance west from Kherson to Odesa was impossible with any acceptable number of dead Russians why, then, the bridgehead in a region whose ethnicity is overwhelmingly western Ukrainian? Without an Odesa victory the Kherson bridgehead just became a running meat-mincer for Russian troops with no strategic gain, and its abandonment is an obvious improvement to Russia’s overall position.

Ample proof that defence trumps attack has been provided over the past 100 days around Bakhmut. Here Russia’s attempt to advance to prevent Ukrainian artillery from firing a daily barrage of shells at civilians in Donetsk has been in full flow since the fall of Lysichansk at the end of July. In spite of a substantial advantage in both artillery weapons and ammunition supplies, Russian forces have advanced at an average pace of only 300 metres per day. Bakhmut has still not fallen even yet.

The fight for Bakhmut is not unusual. In any area where defending forces have been reasonably concentrated (meaning a few hundred men per kilometre) and have been supported by artillery, both sides have found themselves unable to overwhelm a well-prepared defence line. In Kharkiv oblast, after a rapid advance into largely empty space, Ukrainian forces have carried out daily repeated attacks on denser Russian positions without taking any ground, but while suffering mortality rates of 10-20% of the attacking force per attack.

With mortality that high (and another 10-20% of men seriously injured) an attacking unit is effectively expended after a single assault, which may be why the sizes of Ukrainian attacks have shrunk to half-brigades, then quarter-brigades, and now to single companies of a hundred men.

Russia has fared no better. A determined Russian thrust northwards on the village of Pavlivka (40 km south-west of Donetsk) has struggled to make progress and has suffered a mortality rate that appears to be in the range of 3-5%. That may be low compared with Ukrainian loss rates (because Ukraine lacks artillery) but it’s ten times higher than normal Russian mortality rates and therefore probably politically unacceptable to Moscow.

The Pavlivka move may have been a Russian experiment, to test how strongly Ukrainian forces would hold ground. If it was, the answer is that the Ukrainian army has shown itself willing to take appalling losses to prevent Russian advances, and that a major Russian assault over several weeks might win but would see mortality rates of 10-20% of the attacking force.

The lesson does not change for tank attacks. Both sides have re-discovered that tanks are effectively countered by men armed with portable anti-tank guided weapons. Moscow’s daily action reports usually list eight to ten destroyed Ukrainian tanks. Poland’s transfer of 92 tanks to Ukraine last week would last about ten days at that rate. Russia has many more tanks to lose, but each destroyed tank usually kills its crew as well. Again, mortality in a major attack is probably too high for Moscow’s taste.

Stalemate on the ground

In short, the ground war has reached a strategic stalemate. If that is so, then the cession of Kherson may be an embarrassing admission that Odesa is unreachable, but that apart, it is of little strategic significance to Moscow.

The withdrawal from Kherson does, though, free up some forces on both sides for deployment elsewhere. On Russia’s side the force density calculus changes by only a little. The contact line around the Kherson bridgehead stretched for around 200 km. The new one, along the left bank of the Dnipro river, is still 150 km. While a river can be held by fewer men than a line in the steppe, it only forms a tactical obstacle if sufficiently guarded, which means that many of the estimated 40,000 Russians who were in the Kherson bridgehead will have to remain on guard on the new river front.

On the Ukrainian side the density calculus is more favourable. Kyiv had stationed ten brigades around the Kherson bridgehead – 40,000 men. The overwhelming majority of these are now available for deployment elsewhere. They represent a substantial addition to Ukrainian fighting power east of the Dnipro.

At the outset of the war the AFU order of battle contained some 47 infantry and tank brigades. Two of these, the 36th Marines and the Azov brigade, were effectively destroyed in Mariupol. Two more, reserve tank brigades, were probably also destroyed early in the war. Of the remaining 43, Russian contact reports refer to 37 as being engaged on various fronts and contact lines. The other half-dozen are likely stationed on inactive fronts (the border with Belarus, in the Odesa garrison, around Kyiv and north of Kharkiv). What is notable is that we have seen no reports of the formation of new brigades of the AFU.

What that implies is that for all its multiple call-ups the actual fighting manpower of the AFU remains the same now as it was at the start of the war – around 170,000 front-line troops, supported by another 150,000 men in rear areas engaged in logistics, training, administration, internal security, air defence, headquarters, intelligence, equipment repair, on leave and in various stages of medical rehabilitation.

As the rear areas generate a flow of fresh men towards front-line units – maybe a thousand per day – the front line sees a thousand men per day killed. Overall Ukrainian combat power is not growing, but the arrival of 40,000 seasoned troops with high morale across the Dnipro will present a major obstacle to a deeper invasion of trans-Dnipro Ukraine.

Russian reinforcements

Balancing that re-deployment, Russian forces can look forward to a reinforcement seven times larger (in numbers, but less in experienced fighting power). The next question is how will Moscow use that new force? Two options are on offer: one is to concentrate forces and resources for one or two major assaults aimed at completing the destruction of the AFU and the placing of a new Russian frontier along the whole of the Dnipro river.

That option implies the taking of several major cities (Zaporizhye, Kharkiv, Sumi, Kremenchuk, Chernihiv and Dnipro), the occupation of 100,000 sq km of open country and the assumption of civil responsibility for several million civilians in the middle of a war zone (food, energy, medical care, security and housing would all fall to Moscow’s account). It also implies the destruction of an army of nearly 200,000 men who have shown courage and endurance at the highest level.

A major assault would be slow. Months of experience has shown that advances against prepared positions are measurable in a few kilometres per week. Advances are also bloody beyond belief, with an almost-certainty that 20% of Russia’s 300,000 attacking ground forces would die and another 20% be hospitalised over the several months it would take to achieve the aim.

Option two is much less painful. Moscow could use its reinforcements to make its current contact-line effectively impregnable, while completing the occupation of Donetsk oblast, which requires an advance of just 80 km on a 100-km front. Once past the fortress town of Bakhmut the rate of advance might speed up a little, reducing the campaign to perhaps ten weeks at an acceptable cost in lives (many of whom would be LDNR militia, Chechens and Wagner PMCs anyway).

At the end of that campaign Moscow might simply freeze the contact line in place and concentrate on suppressing Ukrainian artillery to prevent it from repeating its eight-year bombardment of civilians in Donetsk from 2014 to now.

That might be a politically acceptable end-point for Russian President Vladimir Putin, if a deeply unacceptable fait accompli for Ukraine's President Volodymyr Zelenskiy. Soldiers and their families on both sides would no doubt quietly welcome it.