Vessels sailing under the United Kingdom Country Flag are required to have on board this flag as part of flag state requirements that derive from maritime regulations in the International Code of Signals and the International Safety Management (ISM) Code. These codes are published by the International Maritime Organization (IMO) as an ongoing effort to reinforce maritime safety procedures and communications to the international maritime community. Fleet management companies and ship owners are responsible to ensure that each vessel in their respective fleets have the appropriate flag signage onboard to be in compliance. This flag is used to identify the flag state a vessel is sailing under and to communicate with other vessels under the provisions of the International Code of Signals.
The United Kingdom Country Flag is represented by two receded red stripes outlined with white stripes, one crossed from the upper hoist (left) corner to the lower fly (right) corner and the other from the upper fly to the lower hoist. Forward stands a cross of larger red stripes outlined with white stripes. There are several versions of the United Kingdom Country flag. The Union flag and Naval Jack appears as a single design, filling the entire flag. The national version is designated to hold a proportion ratio of 1:2, height to length, respectively. The Military version holds a proportion ratio of 3:5. The courtesy flag for civilian ships displays the same design, but it is relegated to the upper hoist quadrant. A red, uninterrupted background fills the rest of the flag. This flag is designated to a proportion ratio of 1:2. A civil Jack displays the design, centered in a white background at a ratio of 1:2, and the naval ensign displays a red cross on a white background and the design in the upper hoist quadrant.