unsinkable aircraft carrier
Military term for a large warship or island base that functions as an aircraft carrier and is considered unsinkable.
The U.S. Navy used that island as an unsinkable aircraft carrier.
空母 is a standard aircraft carrier; 不沈空母 adds the nuance of being unsinkable, often used for island bases.
Compound of 不沈 (unsinkable) and 空母 (aircraft carrier).