Aircraft tail numbers show an aircraft's home country and registration designation. The first letter of the tail number shows the aircraft's country of registration, while the subsequent numbers or letters are the aircraft's individual designation used by air traffic controllers and others when identifying it.
Each country that registers aircraft has its own unique internationally recognized designation. For example, the United States uses "N," the United Kingdom uses "G," and all aircraft registered in Ireland have tail numbers beginning with "EI." After this initial letter is a dash, followed by the aircraft's individual registration designation. Most aircraft in the United States use both numbers and letters, while some nations use one or the other.
Aircraft owners can choose their own aircraft designation, provided the number is not already taken and that it complies with national regulations. For instance, the Nike Corporation registers its aircraft in the United States using the "N1KE" designation.
Older U.S. aircraft had an additional letter after the "N" that described the aircraft's function. Commercial and private aircraft carried a "C" marking, while those for state use had an "S" on their tail numbers. These function letters were discontinued in 1948.
U.S. military aircraft only use numbers to show the aircraft's serial number and model type. Different military branches use additional numbers and letters to show the aircraft's base of operations, squadron or other information.