"If our senior military staff say we have enough troops, enough shells - enough everything - to attack, then we're ready," a Ukrainian serviceman, who identified himself as Mark, told AFP in the Donetsk region this week.
"Who knows when Ukraine will get this chance again," said Mykola Bielieskov, a research fellow at the National Institute for Strategic Studies in Kyiv.
"It's now or never," he told AFP.
Russia was beaten back in embarrassing defeats near the capital Kyiv, Kharkiv and Kherson last year but analysts now say Ukraine has a short window to deliver a larger blow.
Recently conscripted Russian forces are badly depleted after their lackluster offensive, while Kyiv has stockpiled ammunition, taken in long-range artillery and battle tanks from the West and is bolstering its army.
A key question is: when?
"More important than the weather is for Ukrainian troops to master the weapons it was promised from the West and to synchronize intelligence and logistics," said Bielieskov.
He estimated that Ukraine's offensive preparations may culminate by June or July, much later than other forecasts of later this month or early May.
"Everyone in Kyiv understands that an offensive launched prematurely is less likely to succeed," Bielieskov added.
The southern Zaporizhzhia and Kherson regions - that the Kremlin claimed to have annexed last September - are likely targets, and their capture by Kyiv would rupture a land bridge between Russia and the annexed Crimean peninsula.
And when Ukraine does begin its pushback against the fortified Russian positions, artillery and enough shells will be key in a battle dominated by long-range duels.
The European Union last month agreed a two-billion-euro ($2.2-billion) plan to keep Ukraine stocked but observers estimate nearly half of that package would need to be delivered for Ukraine's offensive to succeed.
"Unlike Russians, we are not concerned with the quantity of fire, but the precision of fire. That's how Ukraine plans to make up for this deficit," Bielieskov said.
"The only problem is that we are paying for this in people."
And military recruitment ads throughout Kyiv point to large-scale efforts to build up a new force for the offensive after losses from a year of battle.
Ukraine is also urging Western allies to equip its armed forces with fighter jets to match Russia in the air.
A year after Russia invaded, observers say Ukraine has emerged the more motivated force.
Ukraine Readies for Counter-Offensive
KRAMATORSK, UKRAINE - Ukrainian forces have for months been holding off a Russian offensive in battered towns and heavily shelled trenches along the eastern front line. But now, with the Kremlin's forces making only incremental gains over the winter onslaught, Ukraine is preparing to hit back.