What is "leathernecking"

Leathernecking (1930) is an American pre-Code musical comedy film directed by Edward F. Cline, from a screenplay by Alfred Jackson and Jane Murfin, adapted from the Broadway musical comedy Present Arms, by Richard Rodgers, Lorenz Hart and Herbert Fields.

Although based on a musical, it used only two of the original Rodgers and Hart songs from the Broadway hit, along with original songs, including three by Oscar Levant and Sidney Clare. An early part-color feature film with a Technicolor insert, this film was Irene Dunne's film debut, although no copies of it are thought to exist.