Grand Admiral a naval rank in one of the highest in the several European navies that use this system, what system are they using?
Military rank Military ranks are a system of hierarchical relationships in armed forces, police, intelligence agencies or other institutions organized along military lines. Usually, uniforms denote the bearer's rank by particular insignia affixed to the uniforms. Ranking systems have been known for most of military history to be advantageous for military operations, in particular with regards to logistics, command, and coordination; as time went on and military operations became larger and more complex, military ranks increased and ranking systems themselves became more complex.
Admiral (United States) Admiral (abbreviated as ADM) is a four-star commissioned naval flag officer rank in the United States Navy, the United States Coast Guard, and the United States Public Health Service Commissioned Corps, with the pay grade of O-10. Admiral ranks above vice admiral and below fleet admiral in the Navy; the Coast Guard and the Public Health Service do not have an established grade above admiral. Admiral is equivalent to the rank of general in the other uniformed services. The National Oceanic and Atmospheric Administration Commissioned Officer Corps has never had an officer hold the grade of admiral. However,  /201 § 201  of the U.S. Code established the grade for the NOAA Corps, in case a position is created that merits the four-star grade.