As a cadet, Gordon showed exceptional talents at map-making and in designing fortifications, which led to his choosing to become a Royal Engineer or a "sapper". He was commissioned a second lieutenant in the Royal Engineers on 23 June 1852, completing his training at Chatham, and he was promoted to full lieutenant on 17 February 1854. The sappers were an elite who performed the "reconnaissance work, led storming parties, demolished obstacles in assaults, carried out rear-guard actions in retreats and other hazardous tasks."