From the first of July 2002 the Automatic Identification System (AIS) is introduced as part of the carriage requirements for all ships of 300 CT and larger, falling under the SOLAS convention. An introductory phase is planned to equip these ships with an AIS mobile station. Every ship with AIS, at sea as well as in a VTS environment, will broadcast its position and identity continuously. Further information about ship and voyage is broadcast periodically. AIS is designed to increase safety at sea in a ship-to-ship mode for collision avoidance, as a tool for VTS in the ship-to-shore mode, but also as a means lor littoral States to obtain information about ship and its cargo. The last mode is for interest in a naval environment. AIS can be used during naval operations from ships as well as from the air to investigate sea traffic for monitoring and patrol functions. The paper will describe the naval use of AIS more in detail such as identification to be used by military AIS users, protection (encryption) of data fields in AIS, and special problems with airbotne AIS stations.