Aikman joined the Bengal Army, and went on to serve for eighteen years. He fought in the First Anglo-Sikh War, including being present at the Battle of Sobraon. During the Second Anglo-Sikh War, he was assigned to Major-General Hugh Wheeler's forces until the Indian Rebellion of 1857. During that war, he fought in a number of battles including the Siege of Delhi and the Capture of Lucknow.