The Median Hull Age (MHA) ranking of WDMMW relies on a basic formula taking into account overall hull age related to overall fleet size covering the various naval services of the world. The list below is arranged from youngest overall hull age to oldest with the Japan Maritime Self-Defense Force (JMSDF) taking the top spot ahead of the People's Liberation Army Navy (PLAN) of China. The United States Navy (USN) resides close to the middle of the pack (alongside contemporaries France, Italy, and Spain) with the oldest hulls, not surprisingly, belonging to the Korean People's Army Naval Force of North Korea.