As a code signal the
International maritime signal flag Alpha (or "Alfa", signifying the letter "A") has the meaning of "I have a diver down; keep well clear at slow speed", used to indicate that the vessel has limited maneuverability, and the presence of a diver in the water around the boat. It is used alone in all countries excluding the United States, Canada and sometimes in Italy, but may be used along with the red and white flag, and sometimes the red and white crossed (St Andrews). In the diving culture sphere of influence such as certain countries within the
Caribbean, Australia and North America, it may not be used, and completely replaced with the red and white flag on a buoy or on the boat. Note that the NATO divers uses the St Andrews cross. A rigid replica of the 'Alpha' flag is required to be displayed by any vessel engaged in diving operations when restricted in her ability to maneuver, if the size of the vessel makes it impractical to display the shapes and lights required by the
International Regulations for Preventing Collisions at Sea (IRPCS) Rule 27. ==The red and white flag==