NATO will massively increase its rapid reaction troops from 40,000 to 300,000, says alliance chief Jens Stoltenberg.
He was speaking ahead of a key summit in Madrid later this week that will focus on the response to Russia's war in Ukraine.
It will also consider the bids of Sweden and Finland to join NATO, applications that are a direct result of Moscow's invasion.
Stoltenberg, NATO's secretary-general, said forces on the alliance's eastern flank would be reinforced.
Eight battlegroups have been created: based in Lithuania, Estonia, Latvia, Poland, Romania, Hungary, Slovakia and Bulgaria. They will be reinforced by "pre-designated" units from other alliance countries to operate in these countries where heavy armaments will have been pre-positioned, the NATO chief told a news conference in Brussels.
Stoltenberg also said allies would agree to deliver further military support to Ukraine when they convene for the summit in Spain. He described it as a “strengthened assistance package” including secure communication and anti-drone systems.
Over the long term, Stoltenberg said allies aim to help Ukraine transition from Soviet-era armaments to modern NATO equipment.
NATO will also use the summit to change its language on Russia that in the alliance's last strategy from 2010 was still described as a strategic partner.
"That will not be the case in the strategic concept that we will agree on in Madrid," Stoltenberg said.
"I expect that allies will state clearly that Russia poses a direct threat to our security, to our values, to the rules-based international order."