Pennant number

In the modern Royal Navy, and other navies of Europe and the Commonwealth, ships are identified by pennant numbers (sometimes referred to as pendant numbers). The name pennant number arises from the fact that ships were originally allocated a pennant (flag) identifying a flotilla or particular type of vessel: for example, in the Royal Navy, the red burgee for torpedo boats, H for torpedo boat destroyers. By the addition of a number to the identifying pennant, each ship could be uniquely identified. A pennant number thus consists of letters and numbers. Where a letter precedes a number it is known as a flag superior and where it is a suffix it is known as a flag inferior. Not all pennants have a flag superior.

For the American equivalent, see Hull classification symbol.

For the Canadian equivalent, see Hull classification symbol .

Royal Navy Systems

The system was adopted prior to World War I to distinguish between ships with the same or similar names, to reduce the size and improve the security of communications, and to assist recognition when ships of the same class are together. Traditionally, a pennant number was reported with a full stop "." between the flag superior or inferior and the number, although this practice has gradually been dropped, and inter-war photos after about 1924 tend not to have the full stop painted on the hull. The system was used throughout the navies of the British Empire so that a ship could be transferred from one navy to another...
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