The Japan Maritime Self-Defense Force (海上自衛隊, Kaijō Jieitai
The ship prefix for JMSDF ships is JDS (JMSDF Defense Ship).

History
Following the defeat of Japan during World War II, the Imperial Japanese Navy was dissolved. In the 1947 Constitution, Article 9 specified that "The Japanese people forever renounce war as a sovereign right of the nation and the threat or use of force as a means of settling international disputes." Over the years, the Japanese people have debated over whether this article allows for military forces to be kept for the purposes of self-defense, with the vast majority agreeing. Furthermore, due to the Cold War, Japan's greatest ally, the United States, was also agreeable to the Japanese government providing for a part of its own defense instead of fully relying on American forces. The JMSDF was then formed as the naval branch of the Japanese Self-Defense Force (JSDF) following the passage of the 1954 Self-Defense Forces Law.

Formation
The first ships in the JMSDF were former US Navy destroyers, transferred to Japanese control in 1954. In 1956, the JMSDF received its first domestically produced destroyer since World War II, the Harukaze. Throughout the Cold War, due to the size and power of the Soviet Navy's submarine forces, the JMSDF was tasked primarily an anti-submarine role. It mainly used its large force of destroyers, frigates and anti-submarine warfare (ASW) helicopters for this.

Cold War
Following the end of the Cold War, the role of the JMSDF has been vastly changed. Starting with a mission to Cambodia in 1993, it has been active in a number of United Nations-led peace keeping operations throughout Asia. In 1993, it commissioned its first Aegis destroyer, the DD173 Kongō. Following an increase in tensions with North Korea following the 1993 test of the Nodong-1 missile, the JMSDF has also stepped up its role in theater air defense of Japan. It has also been active in many joint naval exercises with the United States. During the US-led Operation Enduring Freedom, the JMSDF dispatched a number of its destroyers on a rotating schedule to the Indian Ocean in an escort role for allied vessels.

Post Cold War
While the JMSDF is known in particular for its mineclearing capability, MSDF training also emphasizes both antisubmarine and antiaircraft warfare. Defense planners believe the most effective approach to combating submarines entails mobilizing all available weapons, including surface combatants, submarines, aircraft, and helicopters, and the numbers and armament of these weapons were increased in the Mid-Term Defense Estimate. A critical weakness remains, however, in the ability to defend such weapons against air attack. Because most of the MSDF's air arm is detailed to antisubmarine warfare, the ASDF has to be relied on to provide air cover, an objective that competes unsuccessfully with the ASDF's primary mission of air defense of the home islands. Extended patrols over sea lanes are also beyond the ASDF's capabilities.
The fleet's capacity to provide ship-based anti-air-attack protection is limited by the absence of aircraft carriers. The fleet is also short of underway replenishment ships and generally deficient in all areas of logistic support. These weaknesses seriously compromise the ability of the MSDF to fulfill its mission and to operate independently of the United States Air Force and the United States Seventh Fleet. In August 2003, a new "helicopter destroyer" class was requested; the size of the class has most MSDF analysts referring to it as a "helicopter carrier" which would place it in the same realm as the British ship HMS Ocean.
Some have argued that a carrier of any sort would be technically prohibited by the Constitution's pacifist elements, as carriers can be considered offensive weapons. In an April 1988 Diet budget session, however, then Defense Agency chief Tsutomu Kawara said that "The Self-Defense Forces are not allowed to possess ICBMs (intercontinental ballistic missile), strategic bombers, or attack aircraft carriers." Until the 1970s in the US Navy, large-scale flattops had been categorized as "attack aircraft carriers" and small flattops as "antisubmarine aircraft carriers." Since helicopter carriers have little attack capability and are generally slotted into permitted roles including antisubmarine warfare and transport, the government continues to argue that the prohibition does not extend to the new ship.

Capabilities and Recent Developments
The MSDF is commanded by the chief of the maritime staff and includes the maritime staff office, the self-defense fleet, five regional district commands, the air-training squadron and various support units, such as hospitals and schools. The maritime staff office, located in Tokyo, serves the chief of staff in command and supervision of the force. The self-defense fleet, headquartered at Yokosuka, is charged with defense of all waters around the Japanese Archipelago. It commands four escort flotillas (two based in Yokosuka and one each in Sasebo and Maizuru), the fleet air force headquartered at Atsugi, two submarine flotillas based at Kure and Yokosuka, two mine-sweeping flotillas based at Kure and Yokosuka and the fleet training command at Yokosuka.

JMSDF Chief of Staff / Maritime Staff Office

• Self Defense Fleet
  
  
  
  • Fleet Escort Force
    
    
    
    • Escort Flotilla 1
      
      
      
      • Escort Squadron 1
        Escort Squadron 5
        Escort Squadron 61
        Escort Flotilla 2
        
        
        
        • Escort Squadron 2
          Escort Squadron 6
          Escort Squadron 62
          Escort Flotilla 3
          
          
          
          • Escort Squadron 3
            Escort Squadron 7
            Escort Squadron 63
            Escort Flotilla 4
            
            
            
            • Escort Squadron 4
              Escort Squadron 8
              Escort Squadron 64
              Fleet Training Command
              1st Replenishment Squadron
              1st Transportation Squadron
              Fleet Air Force
              
              
              
              • Fleet Air Wing 1 (P-3C UH-60J)
                Fleet Air Wing 2 (P-3C UH-60J)
                Fleet Air Wing 4 (P-3C UH-60J)
                Fleet Air Wing 5 (P-3C UH-60J)
                Fleet Air Wing 21 (SH-60J/K S-61A)
                Fleet Air Wing 22 (SH-60J)
                Fleet Air Wing 31 (US-1A EP-3 OP-3C UP-3D LC-90 U-36A)
                Fleet Squadron 51 (US-1A-kai P-3C UP-3C/D OP-3 SH-60J/K OH-6DA MCH-101)
                Fleet Squadron 61 (YS-11M/MA LC-90)
                Fleet Squadron 111 (MH-53E)
                Fleet Submarine Force
                
                
                
                • Submarine Flotilla 1
                  
                  
                  
                  • Submarine Squadron 1
                    Submarine Squadron 3
                    Submarine Squadron 5
                    Submarine Flotilla 2
                    
                    
                    
                    • Submarine Squadron 2
                      Submarine Squadron 4
                      Submarine Training Command
                      Mine Warfare Force
                      Fleet Research & Development Command
                      Fleet Intelligence Command
                      Oceanographic Command
                      Air Training Command
                      
                      
                      
                      • Simousa Air Training Group (P-3C YS-11TA UH-60J)
                        Tokusima Air Training Group (TC-90 UC-90 UH-60J)
                        Ozuki Air Training Group (T-5 UH-60J)
                        Maritime Materiel Command
                        
                        
                        
                        • Ship Supply Depot
                          Air Supply Depot
                          Training Squadron
                          Communication Command
                          Criminal Investigation Command
                          JMSDF Staff College
                          Maritime Officer Candidate School
                          1st Service School
                          2nd Service School
                          3rd Service School
                          4th Service School
                          
                          
                          
                          
                          • Yokosuka District
                            Kure District
                            Sasebo District
                            Maizuru District
                            Ominato District Organization
                            Each Escort force is formed as an 8-8 fleet of 8 destroyers and 8 on-board helicopters, a modification of the old Japanese Navy fleet layouts of 8 battleships and 8 cruisers. Each force is composed of one helicopter destroyer (DDH) acting as a command ship, two guided-missile destroyers (DDG) and 5 standard or ASW destroyers (DD).
                            
                            First Escort Force - Yokosuka
                            Second Escort Force - Sasebo
                            Third Escort Force - Maizuru
                            Fourth Escort Force - Kure Escort Forces
                            Five district units act in concert with the fleet to guard the waters of their jurisdictions and provide shore-based support. Each district is home to a major JMSDF base and its supporting troops and staff. Furthermore, each district is home to one to two regional escort squadrons, composed of two to three destroyers or destroyer escorts (DE). The destroyers tend to be of older classes, mainly former escort force ships. The destroyer escorts, on the other hand, tend to be purpose built vessels. Each district also has a number of minesweeping ships.
                            
                            District Forces
                            The Fleet Air Force is tasked with patrol, ASW and rescue tasks. It is composed primarily of 7 aviation groups. Prominent bases are maintained at Kanoya, Hachinohe, Atsugi, Naha, Tateyama, Oomura and Iwakuni. The Fleet Air Force is built up mainly with patrol aircraft such as the Lockheed P-3 Orion, rescue aircraft such as the US-1A and helicopters such as the SH-60J. In the JMSDF, helicopters deployed to each escort force are actually members of Fleet Air Force squadrons based on land.
                            
                            Special Forces
                            MSDF recruits receive three months of basic training followed by courses in patrol, gunnery, mine sweeping, convoy operations and maritime transportation. Flight students, all upper-secondary school graduates, enter a two-year course. Officer candidate schools offer six-month courses to qualified enlisted personnel and those who have completed flight school. Graduates of four-year universities, the four-year National Defense Academy, and particularly outstanding enlisted personnel undergo a one-year officer course at the Officer Candidate School at Etajima (site of the former Imperial Naval Academy). Special advanced courses for officers are also available in such fields as submarine duty and flight training. The MSDF operates its own staff college in Tokyo for senior officers.
                            The large volume of coastal commercial fishing and maritime traffic limits in-service sea training, especially in the relatively shallow waters required for mine laying, mine sweeping and submarine rescue practice. Training days are scheduled around slack fishing seasons in winter and summer—providing about ten days during the year. The MSDF maintains two oceangoing training ships and conducted annual long-distance on-the-job training for graduates of the one-year officer candidate school.
                            
                            Recruitment and Training
                            
                            JMSDF Fleet
                            
                            Atago class destroyers (1 in service; 1 launched)
                            Kongō class destroyers (4 in service)
                            Hatakaze class destroyers (2 in service)
                            Tachikaze class destroyers (2 in service) Guided Missile Destroyers (DDG)
                            
                            Takanami class destroyers (5 in service)
                            Murasame class destroyers (9 in service)
                            Asagiri class destroyers (6 in service)
                            Hatsuyuki class destroyers (11 in service) Destroyers (DD)
                            
                            Shirane class destroyers (2 in service)
                            Haruna class destroyers (2 in service) Helicopter Destroyers (DDH)
                            
                            Abukuma class destroyer escorts (6 in service)
                            Yubari class destroyer escorts (2 in service)
                            Destroyer escort JDS Ishikari Destroyer Escorts (DE)
                            
                            Oyashio class submarines (10 in service)
                            Harushio class submarines (7 in service) Submarines (SS)
                            
                            Osumi class LST (3 in service)
                            Yura class LSU/LCU (2 in service)
                            Yusotei class LCU (2 in service)
                            YF 2150 class LCM (2 in service)
                            Landing craft air cushion (6 in service) Amphibious Forces
                            
                            Yaeyama class ocean minesweepers (3 in service)
                            Uwajima class MSC (coastal) (9 in service)
                            Hatsushima Class MSC (coastal) (4 in service)
                            Sugashima Class (coastal) (12 in service) Minesweepers
                            
                            Hyuga class destroyers (1 under construction; more planned)
                            5000t class destroyers (4 planned)
                            2900t class submarines (2 under construction; 2 more planned) Aircraft
                            
                            Imperial Japanese Navy
                            Japanese ship naming conventions
                            Military ranks and insignia of the Japan Self-Defense Forces
                            GlobalSecurity.org - 16DDH "13,500 ton" ton Class