Warrant officer (WO) is a rank or category of ranks in the armed forces of many countries. Depending on the country, service, or historical context, warrant officers are sometimes classified as the most junior of the commissioned officer ranks, the most senior of the non-commissioned officer (NCO) ranks, or in a separate category of their own. Warrant officer ranks are especially prominent in the militaries of Commonwealth nations and the United States.

A midshipman is an officer of the lowest rank in the Royal Navy, United States Navy, and many Commonwealth navies. Commonwealth countries which use the rank include Canada, Australia, Bangladesh, Namibia, New Zealand, South Africa, India, Pakistan, Singapore, Sri Lanka, and Kenya.