 After spending seven years in minor league baseball, Caldwell was called up by the St. Louis Browns.He reappeared successfully on September 22, 1935, outdueling Schoolboy Rowe in a three-hit, 1–0 shutout over the American League leading Detroit Tigers.Caldwell ended with a 3–2 mark and a 3.68 ERA, but faded to a 7–16 with a 6.00 ERA in 1936 and was sent again to the minors.