Mike Mulligan and His Steam Shovel

Houghton Mifflin's house practice of the period is the identifying method, and it is negative rather than stated: the date 1939 appears in arabic numerals on the title page of first printings and is removed on subsequent printings, and the copyright page carries no later-printing statement and no later date (Houghton Mifflin only began consistently printing a 'first printing' statement in the late 1950s)