Since Peter the Great (1682–1725), Russia has had imperial designs on Northern Europe. This is unlikely to change in the foreseeable future. Russia’s tactical-level defeats in eastern Ukraine should not inspire strategic complacency in NATO policymakers. Instead, they should view the entry of Sweden and Finland into NATO as a starting point rather than the finish line.

With Finland now in the North Atlantic Treaty Organization (NATO), and Sweden’s membership forthcoming, NATO needs to act quickly to develop plans that acknowledge the new geopolitical reality in the Baltic. NATO must continuously update its contingency plans to prepare its response to different crises as the security landscape in Europe evolves and new members join the alliance.

In the past, NATO has been too slow to take these steps. After the three Baltic States (Estonia, Latvia, and Lithuania) joined in 2004, the organisation was hesitant to develop contingency plans for them, fearing that to do so might antagonise Russia. This complacency began to change in 2008 after Russia’s invasion of Georgia. NATO did not, however, begin to take its security responsibilities on the eastern front seriously until Russia’s first invasion of Ukraine in 2014.

It is now time to get its plans for the region in order.

The new geopolitical reality in the Baltic impacts domains of land, air, and sea. Finland has an 830-mile border with Russia. Although the Finnish military has adequately defended this border for decades, NATO needs to decide how it will integrate into Finland’s national defense plans. This is true also of Finland’s Åland Islands and Sweden’s Gotland.

There are also big changes in the air domain that need to be addressed. When Sweden joins Finland in NATO, the alliance doubles the number of fourth- and fifth-generation fighters operated by its Nordic member states. NATO already has a well-established Baltic Air Policing mission for the region. With Sweden and Finland in the alliance, NATO will need to upgrade the mission and expand the geographical scope of the existing policing mission to one focused on air defense operations.

The entry of Sweden and Finland will bring maritime changes to the alliance. Combined, both add another 95,775 square miles of an economic exclusive zone and 2,780 miles of coastline. The unique non-militarised status of the Åland Islands brings new challenges to NATO planners. Meanwhile, access to, and use of, Gotland brings opportunities. In addition, the Danish Straits and Denmark’s Bornholm Island will become even more important for its operations in the Baltic. Luckily, both countries have decades, if not centuries, of experience of coastal defense and naval operations in the Baltic Sea. This will enhance NATO’s capabilities in the region.

Not all the strategic spots in the Baltic Sea are part of NATO, as Russia’s Kaliningrad Oblast is also important to regional security. Kaliningrad is a small Russian exclave along the Baltic Sea bordering NATO members Lithuania and Poland. In terms of size, it is slightly larger than Liverpool and has roughly the same population as Cardiff. It plays, however,an outsized role in Russia’s projection of power.

Kaliningrad allows Russia to project military power in the region in a way it would be unable to without access to the exclave. If Moscow wanted to capture the Åland Islands, Gotland, or Bornholm, it would do so from Kaliningrad, which also serves as the cornerstone of Russia’s  military strategy to control access to and within the Baltic Sea region.

If the right steps are taken, Finland and Sweden will help the alliance deter Russian aggression more effectively. The most pressing issue is to help resolve the bilateral issues between Turkey and Sweden that is preventing Stockholm from formally entering the alliance. As July’s NATO Summit in Lithuania approaches, finding a resolution to the stand off becomes a priority.  In addition, the organisation must take steps to update its battle plans for the Baltic Sea region. As part of this process, NATO must factor Kaliningrad into its contingency planning. It cannot carry out any credible defence of the Baltic Sea region without neutralising the threat from Kaliningrad.

Symbolism in international affairs matters. Soon after Sweden joins, the alliance should hold a North Atlantic Council (NAC) meeting on Gotland. The NAC is the principal decision-making body within NATO. The secretary general chairs its meetings. Such a meeting would bring immediate awareness of Baltic Sea security issues to the alliance.

NATO will also need to establish a Baltic Sea Air Defense mission. While the Baltic Air Policing has been useful, more needs to be done. With Russia’s increased aggression, a robust and expanded Baltic Sea Air Defense mission is needed. Air policing alone is no longer enough.

The alliance needs to increase its maritime presence in the Baltic Sea. Under the authority granted in the 1936 Montreux Convention, Turkey has blocked all warships from entering the Black Sea through the Turkish Straits while fighting continues in Ukraine. While the Montreux Convention restrictions are in place, members should divert maritime assets that would have normally been deployed to the Black Sea to the Baltic. Then the alliance needs to develop a longer term plan to maintain a robust maritime presence in the region.

History has shown that most military operations in the Baltic region require access to what is today Swedish and Finnish air, sea, and land. During the Crimean War (1853–56) and the Allied intervention in the Russian Civil War (1918–20), the then Swedish fortress of Viapori (today known as Suomenlinna in Finland) and the Åland Islands played crucial roles. During both world wars, the Danish Straits – which border Swedish waters and serve as a gateway to the Baltic Sea – were highly contested. During the Cold War, Denmark’s Bornholm was an area of contention between the Soviet Union and NATO. These tensions have not disappeared.