which time JMSDF ships started using the prefix JS (Japanese Ship) to reflect the upgrade of the Japanese Defense Agency to the Ministry of Defense. , the JMSDF operates a total of 124 ships (excluding minor auxiliary vessels), including: two multi-purpose operation destroyers (de facto aircraft carriers), two helicopter carriers (called helicopter destroyers), 26 destroyers, 10 small destroyers (or frigates), six destroyer escorts (or corvettes), 22 attack submarines, 29 mine countermeasure vessels, six patrol vessels, three landing ship tanks, eight training vessels and a fleet of various auxiliary ships. The fleet has a total displacement of approximately 624,000 tonnes (excluding auxiliary vessels). Aircraft The Japan Maritime Self-Defense Force aviation maintains a large naval air force, including 201 fixed-wing aircraft and 145 helicopters. Most of these aircraft are used in anti-submarine warfare operations. Aircraft Organization, formations and structure The JMSDF is commanded by the Chief of the Maritime Staff. Its structure consists of 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 commanding and supervising the force. The Self-Defense Fleet, headquartered at Yokosuka, consists of the JMSDF's military shipping. It is composed of Fleet Escort Force (based in Yokosuka, Sasebo, Maizuru and Kure), the Fleet Air Force headquartered at Atsugi, Fleet Submarine Force based at Yokosuka and Kure, Mine Warfare Force based at Yokosuka and the Fleet Training Command at Yokosuka. On 6 March 2018, Ryoko Azuma became the first female squadron commander in the JMSDF. Her unit includes the flagship Izumo, the largest warship in the JMSDF. She commands four warships making up a division with a total of 1,000 crew members. Each Escort Flotilla is formed as a fleet of eight destroyers and eight on-board helicopters. Each force is composed of one helicopter destroyer (DDH) acting as a command ship, two guided-missile destroyers (DDG) and five standard or ASW destroyers (DD). The JMSDF is planning to reorganize the respective Escort Flotillas into a DDH group and DDG group, enabling faster overseas deployments. Prime Minister of Japan Minister of Defense JMSDF Chief of Staff / Maritime Staff Office Self-Defense Fleet Fleet Escort Force Escort Flotilla 1 (Yokosuka) Escort Squadron 1: DDH-183 Izumo; DDG-179 Maya; DD-101 Murasame; DD-107 Ikazuchi (Yokosuka) Escort Squadron 5: DDG-173 Kongō; DD-108 Akebono; DD-109 Ariake; DD-115 Akizuki (Sasebo) Escort