With Russia back on the offensive after significant Ukrainian combat successes around Kharkiv and Kherson in the second half of 2022, the past few weeks have been the bloodiest so far of an already bloody war, with both sides taking extraordinarily heavy casualties. Expect it to get worse.
Ukrainian defence minister Oleksii Reznikov says Russia has mobilised "much more" than 300,000 troops, perhaps up to half a million, and these are pouring into Ukraine in preparation for what is expected to be a major offensive in the coming days and weeks. Although Kyiv has also been building up its forces and supplying them with modern equipment donated by the West, Putin has a much greater advantage in troop numbers than he did when he invaded a year ago. Despite repeated optimistic reports of Russia running low on artillery shells - a battle winner in this conflict - Putin's war stocks are vast, and his factories have been working around the clock to churn out even more.
Under pressure towards the end of last year, Russia withdrew its forces to positions of strength, trading ground for time as it massed resources for a planned hammer blow while grinding down the Ukrainians in the east, softening them up for the assault to come. Much of this has been done by infantry attack, throwing away "expendable" troops in time-honoured Russian style. The Kremlin has at the same time been conserving artillery shells (though expending thousands each day around Bakhmut alone) and the armoured vehicles that are so essential for the fast-moving blitzkrieg Putin is planning.
Until now, the narrative in the West has been that Ukraine is comfortably winning this war, albeit while sustaining heavy bombardments on its major cities. The reality is more complex. The latest estimates suggest that each side may have taken upwards of 120,000 casualties already - hardly indicative of a triumph for Ukraine. And there may be worse to come: the truth is that recent promises of new combat equipment for Ukraine - especially longer range missiles, tanks and other armoured vehicles - are unlikely to be fulfilled in time to have an impact in this battle if Putin launches his offensive on the timetable Kyiv predicts.
With so many more men and resources at its disposal, Moscow will be able to sustain higher casualty rates. This is why Russia tends to do better in wars the longer they go on - it can bring more to bear over time. Even today, Putin does not fear high casualties: disproportionate numbers of his troops are recruited from distant provinces rather than cities such as Moscow and St Petersburg, where a stream of body bags could have some effect on what still remains rock solid support for him and his war.
Another concern is that, while Russian forces have performed abysmally - thwarted by low troop morale, inadequate numbers, badly maintained equipment, clumsy tactics, substandard battle discipline, poor logistics, the stiffest Ukrainian resistance and an unexpectedly united effort from the West - some Ukrainian reports from the front indicate the Russians have been learning hard lessons and making much needed improvements, at least at the level of battle tactics and discipline. The Russian army was bleeding before, but it appointed new commanders and - as in the Second World War - may be recovering from its earlier disasters.
We must therefore be prepared for significant Russian gains in the coming weeks. We need to be realistic about how bad things could be - otherwise the shock risks dislodging Western resolve. The opposite occurred last summer and autumn, as flagging support in parts of Europe and the US was galvanised by Ukrainian success.
It is essential that we not only maintain our combat supplies to Ukraine, but step it up even further and even faster. If Putin gains more ground, then Kyiv will need to counterattack more strongly, and will need more armoured vehicles, better air defences, longer-range missiles and vast quantities of artillery shells and ammunition. The only alternative is that President Zelensky is forced to come to terms, handing victory to Russia and defeat to Ukraine and Nato.
Colonel Richard Kemp is a former infantry commander