求翻译：After the war, Mitchell openly advocated the creation of a separate air force. He claimed that the airplane had made the battleship obsolete. His argument for air power, at the end of the First World War, was so unpopular that he fought for three years for the mere chance to show its effectiveness. He got the chance in 1921, when his superiors let him drop bombs on a captured German battleship to see what damage his novel approach might be able to cause.是什么意思？

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