William Cawthorne Unwin FRS (12 December 1838 – 17 March 1933)[1] was a British civil and mechanical engineer.

He received an education from the City of London School and studied for a year at New College, St John's Wood, many of the universities being closed to him due to his congregational roots.

[3] He returned to Fairbairn's as manager of the engine department in 1856, studying in his spare time to gain a Bachelor of Science degree by 1861.

He also wrote the hydraulics entry for the Encyclopædia Britannica in 1881, an article that was much in demand by engineers of the time and resulted in that part of the Encyclopaedia being much sought after.

He was regarded by Sir Alexander Kennedy as one of the few professors with a full knowledge of the practical aspects of the profession.

[2] Late into his life he remained dedicated to the profession, attending a discussion on impact testing hosted by the Institution of Civil Engineers when he was 82.