The title of this Disney film is misleading. The film's primary focus concerns the lives of a young Confederate soldier, Private Willie Prentiss (Russell) and his Union friend, Corporal Henry Jenkins (MacArthur). The film begins with Willie accidentally shooting an officer he is later to serve under, Lieutenant John Singleton Mosby (Ging). While he initially tries to avoid capture and hanging by both sides (as a spy by the Union and a traitor by the Confederacy), he enters Mosby's service due to his knowledge of the area in which the notorious unit is operating.
The film begins with lots of character development and little involves the historic figure of the title. Eventually, it gets around to portraying Mosby's famous raid in which he captures Union General Edwin H. Stoughton and dozens of prisoners.
The raid, conducted well inside Union territory, was spectacularly successful and ended with no shots being fired. Unfortunately, because Mosby is not the focus of the film, the interesting history is largely glossed over. The film concludes with Corporal Jenkins' romance with Willie's sister, Oralee (Lipton) setting the stage for a Union attempt to trap Mosby's men.
The film's treatment of the Confederates is moderately sympathetic. The primary villain is a spiteful Union sergeant (Adams) who can be counted on to make the expedient decision over the honorable one. Most characters on both sides are reasonably human with the expected flaws. Both Willie Prentiss and Henry Jenkins are confronted with having to decide between friendship and duty.
If the viewer is expecting a good or complete portrayal of the exploits of John Singleton Mosby, it won't be found here. As a family oriented Civil War film, "Mosby's Marauders" is passable, but Disney has done far better with other live action films.