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Instances have been reported where the second or third ship in column in a channel actuated the acoustic mine . The acoustic mine has been developed during the present war . Thus it is , of necessity , a flexible standard which contemplates different mining circumstances . Another problem is that DMME / DMLR 's permitting database has historically classified various mining methods as mountaintop operations regardless of whether an AOC variance had been obtained . Summary : Olsen gives examples of documents reporters usually overlook that actually are gold mines of information .