Satellite images show Russia is using trained dolphins to guard a naval base in the Black Sea, according to a report.

A U.S. Naval Institute report on Wednesday said the Russian Navy placed two dolphin pens at the entrance to Sevastopol harbor, off the coast of Crimea. Satellite images provided to the Washington Examiner by Maxar Technologies show the dolphin pens at the harbor’s entrance, which is being used as a naval base by Russian forces. The pens were placed there around the time of Russia’s Feb. 24 invasion of Ukraine, according to the report.