Finland has constructed underground training fortifications (BASE 25 at Niinisalo and BASE 26 at Säkylä) for platoon-sized units (30-50 troops) to train conscripts, reservists, and military personnel in subterranean combat in response to the threat drones pose for exposed troop movements. The facilities include covered trenches with firing positions, sleeping shelters, vehicle fighting positions, drone-launch openings, steel doors with evacuation hatches as defenses against enemy drones, communications infrastructure, and basic facilities such as dry toilets. Construction uses prefabricated wooden frames covered by logs, rocks, and soil to camouflage and protect from aerial and artillery attacks. The bases serve primarily for training and testing new construction methods rather than immediate wartime use. Exercises last several days, simulating continuous threat conditions, emphasizing psychological resilience and tactical adaptation including retaking temporarily lost positions. Finland’s Pori Brigade’s 3rd Jaeger Company was the first to train at BASE 25 in October 2025 and January 2026 respectively. Construction involves approximately 1.2 miles of trenches with half covered, costing about €2 million (materials and labor). Civilian contractors NCC, Peab, Skanska, and YIT play a central role in wartime fortification construction under prearranged agreements facilitating rapid mobilization of resources and workforce. Additionally, Finland is restoring older coastal fortifications and building modular concrete bunkers drawing on historical defensive lines such as the Salpa Line. This reflects a strategic shift from prior doctrine focusing on mobile warfare to renewed emphasis on permanent defensible terrain and underground protection in an environment increasingly dominated by persistent drone surveillance and reconnaissance threats. The initiative complements a broader European trend to enhance concealment, overhead protection, and psychological endurance under modern combat conditions.

Finland has constructed underground training fortifications (BASE 25 at Niinisalo and BASE 26 at Säkylä) for platoon-sized units (30-50 troops) to train conscripts, reservists, and military personnel in subterranean combat in response to the threat drones pose for exposed troop movements. The facilities include covered trenches with firing positions, sleeping shelters, vehicle fighting positions, drone-launch openings, steel doors with evacuation hatches as defenses against enemy drones, communications infrastructure, and basic facilities such as dry toilets. Construction uses prefabricated wooden frames covered by logs, rocks, and soil to camouflage and protect from aerial and artillery attacks. The bases serve primarily for training and testing new construction methods rather than immediate wartime use. Exercises last several days, simulating continuous threat conditions, emphasizing psychological resilience and tactical adaptation including retaking temporarily lost positions. Finland’s Pori Brigade’s 3rd Jaeger Company was the first to train at BASE 25 in October 2025 and January 2026 respectively. Construction involves approximately 1.2 miles of trenches with half covered, costing about €2 million (materials and labor). Civilian contractors NCC, Peab, Skanska, and YIT play a central role in wartime fortification construction under prearranged agreements facilitating rapid mobilization of resources and workforce. Additionally, Finland is restoring older coastal fortifications and building modular concrete bunkers drawing on historical defensive lines such as the Salpa Line. This reflects a strategic shift from prior doctrine focusing on mobile warfare to renewed emphasis on permanent defensible terrain and underground protection in an environment increasingly dominated by persistent drone surveillance and reconnaissance threats. The initiative complements a broader European trend to enhance concealment, overhead protection, and psychological endurance under modern combat conditions.