In 1918, Pipp hit only two home runs, but batted .304. He missed playing time under the nation's "work or fight" rule during World War I; he worked as a naval aviation cadet at the Massachusetts Institute of Technology. He batted .275 with seven home runs in 1919, as Babe Ruth surpassed him as the best power hitter in the American League. The Yankees moved to strengthen their team after the 1919 season, adding Ruth and fellow outfielder Bob Meusel and third baseman Joe Dugan. Between 1920 and 1924, Pipp had a .301 average, with season averages of 29 doubles, 94 runs scored, and 97 runs batted in (RBI) per season. Led by their strong lineup and additions to the pitching staff, such as Waite Hoyt, the Yankees finished in second place in 1920. Pipp became the cleanup hitter, behind Ruth in the batting order. Pipp hit .296 in 1921, and the Yankees won the American League pennant. However, they lost the 1921 World Series to the crosstown rival New York Giants of the National League.