A leading think tank called on Ukraine's Western allies to show greater faith in its military decisions.
It said Ukraine's decision to attack Russian positions using small groups had been right.
NATO had trained Ukraine to use larger units to make more aggressive attacks on Russian defenses.
Ukraine was right to drop Western-backed plans to attack Russian defenses head-on in large groups, a leading US think tank said.
Instead, the experts noted, Ukraine had found success using smaller units to take on its heavily-entrenched foe.
The Institute for the Study of War on Monday published the assessment of Ukrainian tactics, by analyst Nataliya Bugayova. She argued that the West needed to show more faith in Ukraine.
"The Ukrainian forces have done what successful militaries do — they have adapted and are now advancing. Ukraine recognized the realities of Russian defenses much faster than Western policymakers, who were expecting a rapid Ukrainian breakthrough," said Bugayova.
Her argument echoes that of a US veteran on the ground, who spoke to Insider's Sinéad Baker between training Ukrainian forces.
"If we use American doctrine here, we would definitely have a bad time," said the trainer, who uses the callsign Jackie.
Earlier in the summer Ukraine launched a counteroffensive to breach Russia's formidable defenses in eastern and southern Ukraine.
Its forces uses tactics learned over months in the training camps of NATO armies. The New York Times reported at the time that they involved attacking Russian positions in large groups using complicated maneuvers.
But after suffering heavy casualties Ukraine abandoned that approach. Instead it fell back on more familiar tactics involving smaller groups backed by precision artillery strikes.
Bugayova wrote in a separate assessment in July that the NATO approach was flawed.
"The large-scale mechanized breaches that NATO trained Ukraine's counteroffensive brigades to execute are incredibly difficult and are not the only option available to Ukrainian forces," she wrote. She argued that the Ukrainians were "not failing simply because they are using different approaches.
At the time, some Western military analysts said that Ukraine had been wrong to revert to its old style, and risked dragging out the conflict.
But more recently Ukraine has begun making incremental but important gains in its counteroffensive, which Bugayova attributed to its return to its tried and tested tactics.
"Ukraine's ingenuity is yielding results," she wrote. "Ukraine continues to liberate its territory and people and is slowly but steadily breaking through an incredibly formidable Russian prepared defense — and the Russian forces are unable to stop the advance, which is now moving in two directions," she wrote on Monday.
But other analysts were more skeptical that Ukraine's counteroffensive could yield a decisive result this year. Emil Kastehelmi, a Finnish military analyst, said on Sunday that Russian defensive lines appeared to be "bending not breaking" in the area they were breached.
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