A former Marine, Pennick served not only in WW I and WW II, but also fought in "The Banana Wars", a series of US occupations of such Central American and Caribbean countries as Nicaragua, Honduras, the Dominican Republic and Haiti in the 1920s and 1930s. Re-enlisting in the Marines at nearly 50 years of age during WW II, he received a Silver Star after being wounded in battle.
Appears at the end of She Wore a Yellow Ribbon (1949) (at the party) choreographing the escort squad, in a scene that someone in Continuity should have caught. Clearly knew his military drill.
Originally a horse wrangler, he played small parts in many westerns.
Was an acknowledged expert in military weapons, drills and customs. While filming a picture at West Point, Pennick pointed out that a pair of crossed swords hung in a display at the Army Museum, which had been there for countless years, were upside down. Army officials checked and found out that Pennick was right.
Was known to be an expert in the "manual of arms" for existing and some extinct military units. Can be seen marching as "right guard" at the very beginning of Stars and Stripes Forever (1952), uncredited.
Worked in nearly every sound picture directed by John Ford as part of "The John Ford Stock Company".