Flag alphabet

Ships use the flag alphabet to exchange messages. They do this optically, using signal flags. There are different ways in which this can be done:

• Each flag can represent a letter, all the flags spell out the message
• A flag used alone usually has a special meaning. A boat supporting a diver will show the "A flag"
• Several flags used together can form a code, which can be looked up in a code book both ships have.
• In ship races, flags have different meanings:

Two ships with signalling flags