This is the 12280th most frequent Polish word.
militarnego
"Militarnego" means "military" (relating to the military).
Here, 'militarnego' modifies 'zagrożenia', signifying that the threat is related to military matters.
Wojsko przeprowadziło symulację militarnego zagrożenia.
The army conducted a simulation of a military threat.
In this usage, 'militarnego' describes 'ćwiczenia', referring to the exercise being of a military nature.
Podczas ćwiczenia militarnego żołnierze udoskonalali swoje umiejętności.
During the military exercise, soldiers improved their skills.
Here, 'militarnego' qualifies 'budynku', indicating the building is associated with military functions or use.