General Order No. 541 (1920)
Following World War I, and the confusion experienced in mailing correspondence and shipping spare parts to ships, Acting Secretary of the Navy Robert E. Coontz approved a standardized system of alpha-numeric symbols to identify ship types (e.g., BB for battleship, DD for destroyer, DM for light mine layer, AD for destroyer tender). Linked with a consecutive number, the use of which now became general for all types of naval ships, these classification symbols provided positive and individual identification of both named and unnamed ships, many of which might not be readily identifiable by name alone.
Note that while the first letter of the ship type indicates the type designation, and the second letter indicates sub-type (such as CL for light cruiser), this is not always the case as shown by the designation DD, which simply stands for "destroyer" and ODD, which stands for "old destroyer."
OFFICE OF NAVAL OPERATIONS,
Washington, D.C., July 17,1920.
STANDARD NOMENCLATURE FOR NAVAL VESSELS
1. In order to provide a standard nomenclature for types and classes of vessels comprised in the U.S. Navy, as well as a standard system of identification numbers which may be used, when pertinent, in correspondence and for the marking of spare parts and the like, there will be published annually a "Ships' Data Book," prepared by the Bureau of Construction and Repair and approved by the Secretary of the Navy, which will contain the standard nomenclature, identification numbers, and abbreviations for naval vessels. Such nomenclature, numbers, and abbreviations shall be used in official correspondence and communications and for the marking of spare parts.
In advance of the issue of the next "Ships' Data Book," which will contain the approved standard designations, including identification numbers of all naval vessels, the following detailed list shows the names of types, type designations, names of classes, and class designations to be included in future editions:
|Type||Type Designation||Class||Class Designation|
|Battleship||B||Battleship, first line
Battleship, second line
Monitor, first line
Monitor, second line
|Cruiser||C||Battle cruiser, first line
Battle cruiser, second line
Cruiser, first line
Cruiser, second line
Light cruiser, first line
Light cruiser, second line
Aircraft carrier, first line
Aircraft carrier, second line
Minelayer, first line
Minelayer, second line
|Destroyer||D||Destroyer, first line
Destroyer, second line
|Submarine||S||Submarine, first line
Submarine, second line
Fleet submarine, first line
Fleet submarine, second line
Lighter-than-air craft tender
Heavier-than-air craft tender
Torpedo and bombing plane
|District Craft||Y||Ash lighter
Ferry boat and launch
Torpedo testing barge
NOTE.--Vessels taken over temporarily by the Navy will have will have designating letters and numbers assigned according to the type and class to which they belong. The Identification numbers for such vessels will always be preceded by the letter "X," Indicating the temporary nature of the assignment; for example, if there were already four heavier-than-air craft tenders In the Navy and a fifth were taken in temporarily, It would be given an identification number XAV5. The number "5" should not be again used for vessels of this class; the next heavier-than-air craft tender built or taken over would be "6."
R. E. COONTZ,
Acting Secretary of the Navy.
Dr. Timothy L. Francis, 10 August 2007