Pitching in minor league baseball, Pennock began to regain confidence. However, Boston manager Jack Barry used Pennock sparingly in the 1917 season, and Pennock enlisted in the United States Navy in 1918. Pennock pitched for a team fielded by the Navy, defeating a team composed of members of the United States Army in an exhibition for George VI, the King of England, in Stamford Bridge. After the game, Ed Barrow, the new manager of the Red Sox, signed Pennock to a new contract after promising to use him regularly during the 1919 season.