military secret; classified military information
Refers to confidential military plans, documents, or information. Often used in contexts of national security or espionage.
An investigation was conducted on suspicion of leaking military secrets.
Acts violating the Military Secrets Protection Act are severely punished.
military aircraft
A less common, somewhat dated term for military aircraft. Modern usage tends to prefer 軍用機 (ぐんようき).
Military aircraft of the former Japanese army are on display.
The spy was arrested on suspicion of leaking military secrets.
Soldiers have a duty to protect military secrets.
軍用機 is the standard modern word for a military aircraft, while 軍機 in this sense is a rarer, somewhat dated alternative.
軍機 (ぐんき) means a military secret or military aircraft, while the identically pronounced 軍紀 means military discipline or regulations.
Compound of 軍 (ぐん, 'military') and 機 (き, 'machine' or 'secret'). The 'military secret' sense derives from the meaning 'secret' of 機, while the 'military aircraft' sense derives from the abbreviation of 軍用機 (ぐんようき).