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https://en.wikipedia.org/wiki/Target_ship#As_exercises
The US military term Sink Exercise (SINKEX) is used for the test of a weapons system usually involving a torpedo or missile attack of an unmanned target ship. The US Navy uses SINKEX to train its sailors on the usage of modern-day weapons.[7]

This technique is used to dispose of decommissioned warships.
撃沈演習（SINKEX)は退役艦の処分方法として用いられる