Doctor William Gunn had a long and varied career in the Royal Navy. After spending time on anti-slavery patrols along the west coast of Africa, he was posted to the south Pacific. At Pitcairn Island, he treated the inhabitants during an influenza epidemic, proving himself to be a determined and dedicated practitioner. Subsequently, he was appointed head of the medical department at Chatham Royal Dockyard (1859-1865), an appointment that coincided with the final stages of the Royal Navy's transition from sail and wood to steam and iron. The impact of these changes on the health of dockworkers was quickly felt at Chatham, and Gunn found himself in charge during the building of the first iron warship in a royal dockyard. His story thus offers a window through which to observe a practitioner confronting the health issues and medical uncertainties thrown up by technological change in the Victorian era.