A rigid replica of the 'A' 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 Rules for Prevention of Collisions at Sea (IRPCS) Rule 27.[6][7]
Although the presence of the 'A' flag may afford some protection for divers in the vicinity of the vessel displaying the flag, the intention of the rigid replica required by IRPCS Rule 27 (e) is to warn other vessels of the danger of collision. This marks a distinction between the 'A' flag and the red and white diver down flag.[8]