Ukraine needs rapid training for recruits and more anti-tank and anti-missile weapons to stop Russia's larger military from grinding it down, British analysts say.
A report by British military think tank Rusi said Russian President Vladimir Putin's forces could wear their Ukrainian opponents down despite their resolve, clumsy Russian planning and western military aid.
It said the next phase of support should allow Ukraine to weaken Russia's forces rather than merely bogging them down in a war of attrition in which Moscow may gain the upper hand.
This should involve giving Ukraine multiple-launch rocket systems and anti-radiation missiles to defeat the Kremlin's electronic warfare systems, analysts Jack Watling and Nick Reynolds wrote.
“The support that has enabled Ukraine to survive … will not deliver an end to the conflict,” they said.
“Russia could still wear down Ukrainian ammunition stockpiles, its reserve of skilled troops and the patience of the international community to slowly claw back a path towards meeting its aims.”
The analysts said Russia's numerical superiority was important because Ukraine was short of both skilled infantry and of higher-ranking staff who could organise complex counter-attacks.
As a result, Ukraine's armed forces should “receive training at scale” — and in a less piecemeal way than takes place when each western donor gives lessons in how to use whatever equipment it is providing, they said.
Nato and its members credit the pre-war training they gave Ukrainian forces with aiding the country's resistance to the Russian invasion.
But the analysts said this should be expanded so that Ukraine can swiftly form units and send them into counteroffensives to regain territory.
At a higher level, Ukraine's sometimes improvised defensive tactics would not be easy to replicate on a wider scale without extra staff training, and “make the transition from defence to offence challenging”, they said.
Russia on Monday claimed one of its most significant military successes during the four-month war by capturing the city of Lysychansk, the last major Ukrainian-held city in the Luhansk region in the east.
Mr Putin hailed what he called the liberation of the area, which British intelligence said it expected to be followed by a renewed assault on the neighbouring Donetsk region.
Capturing both regions would give Russia control of the Donbas, a partly Russian-speaking area where Moscow refocused its offensive after it failed to seize Kyiv, and a central part of Mr Putin's justification for the war.
To turn the tide, Ukraine must be able to weaken Russia's ammunition supplies by firing at them with 155mm howitzers, shells and rockets, the Rusi analysts said.
“The current approach by which each country donates a battery of guns in a piecemeal way is rapidly turning into a logistical nightmare for Ukrainian forces with each battery requiring a separate training, maintenance and logistics pipeline,” they said.
“In breaking up the Russian fire complex, targeting ammunition would significantly reduce the volume of fire that Russia could bring to bear and thereby offer advantage to the force able to strike with greater precision.”
Britain claims Russia lacks precision in its rocket strikes, partly because its dwindling stockpiles have forced it to turn to less sophisticated Soviet-era weapons, thereby causing civilian casualties.
The US said it is providing multiple-launch rocket systems but has sought assurances from Ukraine that long-range weapons will not be used, as they theoretically could be, to hit Russian territory.
Further requirements for Ukraine to win the war would include anti-tank guided weapons, man-portable air-defence systems, secure communications and ways of disrupting Russia's electronic warfare, the report said.
Russian communications have been panned by western officials after they were intercepted by Ukrainian forces and amateur listeners, but Ukrainian Motorola radios are also susceptible to jamming and decryption, the analysts said.