Grimes and O'Brien are the two sons of John Wayne, the Cahill of the title. Feeling neglected by a father who travels extensively, the pair get involved with a bank robbery that has serious consequences beyond what the two anticipated. I am not certain how much credit goes to McLaglen, or to cinematographer Joe Biroc, but what makes Cahill more interesting than the plot description might suggest is the visual style of the film. There are many shots from a child's eye level, emphasizing the difference in size between the men and the boys. Terror is conveyed with shots of Kennedy emerging from the dark, or in a scene in a graveyard where the boys are photographed from above. McLaglen's previous films were usually shot by William Clothier. In Cahill there is a precision about the framing of shots and blocking of actors that does not appear in McLaglen's earlier films with John Wayne.

As a John Wayne vehicle, Cahill is of more limited interest. There is amusement in seeing actors from previous films associated with Wayne or McLaglen such as Hank Worden, Harry Carey, Jr., and Denver Pyle. It also doesn't take a sharp eye to spot Chuck Roberson doing much of Wayne's stunt riding. Kennedy and his gang of thugs have the most fun, a group of good ol' boys who happen to be bank robbers and killers on the side. George Kennedy has the best lines in Cahill which suggest his kinship to Robert Mitchum in Night of the Hunter. At one point finding that he cannot come to an agreement with one of the Cahill sons, Kennedy declares, "The trouble with you, boy, is you have no grace. You should allow a man his illusions."