The red patch dates back to the early days of WWII during the Battle of Guadalcanal. After the initial assault on the beachhead, follow-on troops came ashore and confusion on the beach led to landing support Marines (then known as shore party) and infantrymen getting mixed together. Some shore party Marines went inland along with infantry battalions, while some infantrymen were left behind on the beach. It is not known for certain who made the decision, but a device was created in order to distinguish the shore party Marines: a red patch on the trousers and hat, referred to by Marines as a cover, (a patch was not put on the blouse because many Marines did not wear them due to the heat of the South Pacific). Around the same time, Naval Shore Parties, now known as Beachmaster Unit One began to wear yellow patches on their uniforms, as they do today.
