Surgeon Rear-Admiral Charles Marsh Beadnell (17 February 1872 – 27 September 1947), best known as C. Marsh Beadnell, was a British surgeon and Royal Navy officer. Beadnell was born in Rawalpindi. He was educated at Cheltenham College and studied medicine at Guy's Hospital. He was a Fellow of the Chemical Society and of the Royal Anthropological Institute. A rationalist and sceptic, he was president of the Rationalist Press Association (1940–1947). Beadnell described himself as a "devout agnostic". He died in Petersfield, Hampshire.