Yet these efforts have resulted not in a unified force, but in a motley collection of units of widely varying ability — the volunteer National Guard formations under the Interior Ministry and the regular army units under the Ministry of Defense — with only a weak central command structure.

That lack of cohesion cost the Ukrainian forces dearly in late August.

Sgt. Maj. Igor Tchaikovsky, 47, an army veteran who joined the volunteer Donbass battalion, said a lack of proper equipment and backup had cost his unit dearly, with about 50 men killed, 40 wounded and 110 taken prisoner when they withdrew from the town of Ilovaysk on Aug. 29.

“We got the order to leave, and were told there was a corridor,” Sergeant Major Tchaikovsky said. “We made our column with civilian cars; we don’t have military vehicles or heavy guns. We had a big civilian truck loaded with wounded, and pickups and small cars.”

After traveling 18 miles, he said, the column came under attack from Russian artillery and antitank grenades. “We managed to scatter and started fighting,” Sergeant Major Tchaikovsky said. “Normally, volunteer battalions function like police. This fighting was not something we should be doing.”

He said that the battalion had been able to capture some vehicles and eight prisoners, some of them Russians, but that its route out had been blocked. Surrounded, the battalion was forced to surrender, he recalled. The Russian troops immediately exchanged some of the wounded Ukrainians for their own men, and then turned the rest of their captives over to the separatist rebels, he said. He and a handful of others were later released in another prisoner exchange, but 99 soldiers are still being held in the basement of the Security Service headquarters in Donetsk.

Despite the losses and the scale of the Russian intervention, soldiers interviewed over the past two weeks insisted that Ukraine had to build up its forces and continue to resist any breakup of Ukrainian territory.