A sub-lieutenant is a junior officer rank in many navies and some air forces. They typically hold a position just above an ensign or equivalent rank and are responsible for assisting in various duties, including navigation, operations, and training of lower-ranked personnel. Sub-lieutenants often serve on ships or in aviation units, gaining experience for future promotions. In the military hierarchy, sub-lieutenants are crucial for leadership development. They may lead small teams and participate in planning and executing missions. This rank is essential for building skills necessary for higher ranks, such as lieutenant or captain.