Karen Cahill joined the Royal Navy in 1994 after completing a Bachelor of Arts with honors in teaching. As a surface warfare officer her sea-going units included the frigates HMS London and Grafton, destroyers HMS Cardiff and Nottingham and aircraft carrier HMS Invincible. Ashore she worked in the Ministry of Defense headquarters developing discipline policy, on the Combined Maritime Forces staff and as commanding officer of the Diego Garcia UK military contingent. She also served on the British Peace Support Team (Africa) developing maritime capability. Before joining the Naval War College faculty she served in the U.S. Central Command operations directorate.