Lighthouse and naval vessel urban legend

The lighthouse and naval vessel urban legend describes an encounter between a large naval ship and what at first appears to be another vessel, with which the ship is on a collision course. The naval vessel, usually identified as of the United States Navy or Royal Navy and generally described as a battleship or aircraft carrier, requests that the other ship change course. The other party (generally identified as Canadian or often Irish and occasionally Spanish) responds that the naval vessel should change course, whereupon the captain of the naval vessel reiterates the demand, identifying himself and the ship he commands and sometimes making threats. This elicits a response worded as "I'm a lighthouse. Your call" (or similarly), a punchline which has become shorthand for the entire anecdote.