The U.S. Army needs more horses for the Spanish-American War. Hoppy must turn his Bar 20 cowhands into Rough Riders to gather up the horses, and of course bad guys try to sabotage the operation.

William Boyd
as Hopalong Cassidy

Russell Hayden
as Lucky Jenkins

George 'Gabby' Hayes
as Windy Halliday

Judith Allen
as Barbara Allen

Billy King
as Boots

Alexander Cross
as Black Jack Carson

Karl Hackett
as Major McCready

Bob Kortman
as Hawks

Jack Rockwell
as Shorty

John Beach
as Smokey