In the event of an attack on one of NATO’s member states, the remaining countries are obligated to come to its defense. Article 5 of the NATO treaty has been invoked only once in history—in 2001, following the terrorist attacks on the World Trade Center. However, there is still no practical experience in applying it in the context of a conventional war. The Loyal Leda 2026 exercise at the NATO Joint Force Training Centre  was designed to address how to prepare for such a scenario.

“Loyal Leda 2026 strengthened NATO’s readiness, our interoperability, and mutual trust,” assessed Major General Bogdan Rycerski, Commander of JFTC. Approximately 4,000 soldiers from nine countries participated in the exercise, along with around 1,000 civilian experts.

Commands from four corps took part. Two of them—the Multinational Corps Northeast (Szczecin, Poland) and the NATO Rapid Deployable Corps – Spain (Valencia, Spain)—successfully completed the exercise by passing the Combat Readiness Evaluation (CREVAL). The 1st German/Netherlands Corps (Münster, Germany) and the 2nd Polish Corps (Kraków, Poland) were trained to conduct operations beyond the scope of major joint operations. The JFTC, located in Bydgoszcz, served as the main coordinator of the exercise.

On the website of NATO’s Allied Command Transformation, it was explicitly stated that the Loyal Leda 2026 scenario was based on the application of Article 5, meaning a potential act of aggression against NATO. The aim was to help verify procedures in the event of a threat and support NATO’s transformation so that the alliance remains adapted to current geopolitical challenges. However, the identity of the hypothetical aggressor was not disclosed. The exercise took place from March 3 to 12.