In 1978, the USS Stein (a United States Navy Knox-class destroyer escort) was running special operations in the Pacific Ocean when it encountered something large and unseen in the water. Completely out of nowhere, the ship began to experience technical issues and eventual failure of its SONAR system (a technique that uses sound propagation to navigate and detect objects under the surface of the water), a problem which required the ship to return to port in San Diego, California.