In the modern Royal Navy

Royal Navy

The Royal Navy is the naval warfare service branch of the British Armed Forces. Founded in the 16th century, it is the oldest service branch and is known as the Senior Service...

, and other navies of Europe

Europe

Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...

 and the Commonwealth

Commonwealth of Nations

The Commonwealth of Nations, normally referred to as the Commonwealth and formerly known as the British Commonwealth, is an intergovernmental organisation of fifty-four independent member states...

, 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

Pennon

A pennon was one of the principal three varieties of flags carried during the Middle Ages . Pennoncells and streamers or pendants are considered as minor varieties of this style of flag. The pennon is a flag resembling the guidon in shape, but only half the size...

 (flag) identifying a flotilla or particular type of vessel: for example, in the Royal Navy, the red burgee

Burgee

A burgee is a distinguishing flag, regardless of its shape, of a recreational boating organization.-Etiquette:Yacht clubs and their members may fly their club's burgee while underway and at anchor, day or night, but not while racing. Sailing vessels may fly the burgee from the main masthead or from...

 for torpedo boat

Torpedo boat

A torpedo boat is a relatively small and fast naval vessel designed to carry torpedoes into battle. The first designs rammed enemy ships with explosive spar torpedoes, and later designs launched self-propelled Whitehead torpedoes. They were created to counter battleships and other large, slow and...

s, H for torpedo boat destroyers. By the addition of a number to the identifying pennant, each ship could be uniquely identified.