top-secret

Modifies a noun

• mission: Synopsis: The British armed forces unveil a plan for a top-secret mission that is to take place inside occupied France.
• laboratory: In a top-secret military laboratory, scientists are struggling to defeat man's oldest rival.
• facility: The country, already embroiled in a bloody war, has invested £ 300m in a top-secret nuclear weapons facility.
• document: One indication of the widespread concern about this is the leaking of a top-secret document from the secret services last week.
• base: According to my research a top-secret military base now exists at Ultima Thule akin to S4 at Area 51 in Nevada.
• project: Did you get the plans for the top-secret rocket project I sent you?