NATO: Reinforcing its eastern flank

According to NATO, there were no NATO forces in the eastern part of the Alliance before 2014.

Russia’s annexation of Crimea in March 2014 was a “wake-up call” for the Alliance. At its summit in September that year, NATO said “Russia’s aggressive actions against Ukraine have fundamentally challenged our vision of a Europe whole, free and at peace.”

The Alliance agreed what the Secretary General described as the “most significant strengthening” of its collective defence in decades.

The Readiness Action Plan

In 2014 NATO adopted the Readiness Action Plan, a package of measures designed to assure allies, improve the responsiveness and effectiveness of its forces, and deter threats. More measures were agreed at subsequent ministerial meetings and summits, most notably in Warsaw in 2016.

Some of the most visible measures have been:

  • The deployment of four multinational battlegroups in Estonia, Latvia, Lithuania and Poland
  • A significantly enlarged Response Force of 40,000 troops
  • A new 5,000 strong very high readiness force to deploy at short notice
  • Expanded air policing above the Baltic States and in the southeast
  • Increased naval presence in the Black Sea
  • New commands to maintain lines of communication across the Atlantic Ocean and facilitate the movement of troops and equipment across Europe
  • New small units in eight countries bordering Russia, Ukraine and the Black Sea to facilitate the deployment of the new very high readiness force.

In the Baltic States: new battlegroups and enhanced air policing

In the immediate aftermath of the military incursion into Ukraine in 2014, NATO boosted its air defence and air surveillance capabilities. The Baltic air policing mission was expanded, with a second base in Estonia (Ämari Air Base) added to the original base in Lithuania (Šiauliai Air Base).

RAF Typhoon aircraft have participated in the Baltic air policing mission five times since 2014; three times in Estonia (2015, 2016 and 2019) and twice in Lithuania (2014 and 2020).

The UK is leading one of the three battlegroups established in the Baltic States since 2017. As of March 2021, there were approximately 4,000 troops across all three battlegroups. The UK-led contingent in Estonia is currently based around the Royal Tank Regiment.

NATO battlegroups (PDF) include main battle tanks, amoured fighting vehicles, self-propelled artillery and air defence assets, bomb disposal engineers and intelligence, surveillance and reconnaissance specialists, among other capabilities. 


The US leads a fourth multinational battlegroup in Poland. In March 2021 this numbered around 1,000 troops (PDF), including a light cavalry squadron from the Royal Dragoon Guards.


NATO has reinforced air policing in Romania, covering NATO’s south-eastern flank along the Black Sea. The UK contributed four Typhoon aircraft to Romania for NATO’s southern air policing mission in 2017 and 2021.

In March 2014, NATO began flying air surveillance missions over Poland and Romania to monitor the Ukraine crisis.

An expanded Response Force

Since 2014 NATO has significantly enhanced its existing Response Force, increasing total troop numbers from 13,000 to 40,000.

Air, land, maritime, Special Forces, and logistics troops from across the Alliance have been placed on a high level of readiness and are available to support the response force in 2022 if required. NATO will not disclose the exact composition or locations of these forces for reasons of operational security.

NATO has also created a smaller very high readiness force of 5,000 troops as part of the Response Force. France is leading the force in 2022, which will be built around the Franco-German brigade (a bi-national unit) of 3,500 troops, with additional forces from Spain, Portugal and Poland. 

In January 2022, the US announced 8,500 US-based military personnel have been placed at readiness to “provide forces if NATO should activate the NRF [NATO Response Force] or if other situations develop”. These forces remain in the United States.

The Response Force has never been activated in its entirety since it was established in 2003. However, elements have been activated in response to natural disasters and most recently, to assist with the evacuation of Afghans from Afghanistan in August 2021.

Will there be further deployments in response to the Ukraine crisis?

Following the meeting of the NATO-Russia Council on 12 January 2022, the NATO Secretary General said that in the event of any Russian use of force against Ukraine, the alliance would “have to seriously look into the need to further increase our presence in the eastern part of the Alliance”.

Initial moves to reinforce “allied deterrence” were announced on 24 January 2022. Several NATO nations, including Spain, Denmark, and the Netherlands will deploy additional fighter aircraft and naval assets to Eastern Europe and the Baltic Sea as part of NATO’s Enhanced Forward Presence in the region. France has indicated its “readiness” to send troops to Romania under NATO command and the Netherlands is putting forces on standby for NATO’s Response Force.

On 30 January Downing Street said the UK is considering bolstering its offer to NATO with a major military deployment. The press release said the UK is considering options to double troop numbers and send defensive weapons to Estonia. The Prime Minister has also suggested the UK may reinforce the NATO battlegroup in Estonia and sending RAF Typhoon fighters and Royal Navy warships to southeast Europe.The MOD is sending Royal Marines and Royal Engineers to Poland on a bilateral basis.

On 2 February the US announced plans to send an additional 3,000 troops to Romania, Poland and Germany to “reinforce the deterrent and defensive posture on NATO’s eastern flank.” The US had previously put 8,500 troops (based in the US) at readiness to “provide forces if NATO should activate the NRF [NATO Response Force] or if other situations develop”.

On 7 February 2022 NATO’s Secretary General said the Alliance is “considering more longer-term adjustments to our posture, our presence in the eastern part of the Alliance. No final decision has been made on that.” 

The Russian perspective: NATO is breaking its promises

Russia has long blamed NATO for breaking perceived promises Moscow believes NATO made after German reunification in the 1990s to not expand further. In late 2014, Russia cited the build-up of military infrastructure near the borders of the Russian federation as one of the reasons for identifying NATO as an external risk to Russia.

About this paper and further reading

This paper discusses how and where NATO has boosted its presence along its eastern flank; in the countries that border Russia, Ukraine and the Black Sea. Discussion of US and western military support to Ukraine can be found in Commons Library paper Military Assistance to Ukraine, SN07135.

A more detailed analysis of NATO/Russia tensions regarding Ukraine can be found in Commons Library paper Ukraine: Russia’s red line, CBP9401. Diplomatic efforts in January 2022 are discussed in European security: The outcome of talks with Russia, CBP9425.

Previous NATO decisions are discussed in more detail in NATO Wales Summit 2014, SN06947, and Russia: November 2016 update, CBP7276.

Commons Library paper What is NATO?, CBP9426, provides a simple introduction to the Alliance.


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NATO: Reinforcing its eastern flank