Don Horwood

Don Horwood was a member of the Post Office team that built Colossus, the electronic computer developed at the Post Office Research Station at Dollis Hill to help decode encrypted German Lorenz cipher traffic during the Second World War. He and colleague Harry Fensom reassembled the Mark 1 Colossus prototype at Bletchley Park after its January 1944 delivery, and the machine was working within weeks. In 1973 he authored a technical description of the machine's design, a document that remained classified until 2003.