Undercover, also known as Undercover: How to Operate Behind Enemy Lines and How to Operate Behind Enemy Lines, is a 1943 Office of Strategic Services training film, directed by and featuring John Ford. It was edited by Ford’s longtime collaborator Robert Parrish.

Undercover was Ford’s only sound film acting role, and was the first film ever produced by an intelligence service to train its agents. The film, which is in the public domain, is now widely available online since it was declassified after the war, and it often goes unmentioned in Ford filmographies.