A mackintosh is not the same thing as a trench coat. A Mackintosh or Mac is a raincoat made from a rubberized fabric, initially invented by a Scottish chemist named Charles Macintosh in the early 19th century. A trench coat is a more modern piece of attire, its invention dates back to First World War. The design of this waterproof overcoat was developed by British Army for soldiers involved in the war effort in the trenches.