Air Defense: Japanese ASEVs


September 27, 2023: Japan wants to build two seagoing BMD (ballistic missile defense) ships and is faced with two options. The first, which was discarded, was a ship design that only contained the Aegis BMD radar and Aegis system BMD missiles. That would be the sole purpose of these ships. Instead, Japan decided to build two more Maya-class destroyers with additional BMD capabilities. Japan is calling these modified destroyers ASEVs (Aegis system equipped vessels). This is part of the Japanese effort to expand its ballistic missile defenses. Most of these will still be based on the Aegis system, which is normally installed on large (8,000 tons and up) warships. Japan has eight Aegis anti-missile system destroyers but was unsuccessful in placing Aegis Ashore in Japan. There was too much local civilian opposition. Civilians do not object to Aegis equipped ships. Not all the Japanese Aegis destroyers are the same. There are two Maya-Class ships, two Atagos and four Kongos. By 2030 Japan plans to have twelve Aegis equipped warships. Japan was unsuccessful in getting the ASEV ships built. These are 12,000 -ton ships that are 620 feet long and 82 wide and are armed with 128 VLS cells each containing an antiaircraft or BMD missile. A dozen or so cruise or anti-ship missiles are also carried. ASEV has a crew of 240 and a top speed of 58 kilometers an hour. There is an Aegis radar and fire control system to quickly launch the right missile at targets detected by the radar. Working with the radar is ECM (Electronic Countermeasures) that detects electronic threat and an electronic jammer to disrupt that threat if the chaff and decoys do not work. There is one five-inch gun, and a helicopter flight deck with a hangar for one helicopter.

While the Japanese destroyers are smaller than the ASEV, their armament is more diverse and capabilities more extensive, which requires larger crews, usually 300 sailors. The destroyers are faster, can travel farther from Japan and more expensive to build and operate than the ASEV. Despite that the first two ASEVs will cost more than a destroyer because of development costs. If Japan builds more ASEVs they will be cheaper than destroyers. The Navy would rather have more destroyers because the ASEV is more of an Aegis system platform than a traditional destroyer.

The Maya class destroyers are improved versions of the earlier Atago class. The Mayas also borrow much from the first four Japanese Aegis-ABM ships, the 9,500-ton Kongos, which were built during the 1990s and modeled on the American Burke class Aegis destroyers. The Kongos have 90 VLS (Vertical Launch System) cells for anti-aircraft/missile missiles as well as ASROC anti-submarine rockets that carry an anti-submarine torpedo to, in effect, extend the range of the torpedo by 22 kilometers. Japanese Burke type destroyers also carry a five-inch gun and eight Japanese designed anti-ship missiles which are similar to the American Harpoon. The Maya class has 96 VLS cells (as does Atago) as well as more advanced electronics that enable the Mayas to link with the U.S. Navy CEC (Cooperative Engagement Capability) that allows real-time sharing of sensor and other data in real-time between other CEC equipped ships and even shore-based systems like Aegis Ashore.

The two land-based Aegis Ashore anti-missile systems were not expected to be in service until 2024, but popular opposition caused the ashore program to be terminated. The ASEV was developed to do what Aegis Ashore was intended to do but won’t be in service until 2027 and 2028. ASEV can operate from coastal waters or a harbor as well as on the high seas to protect the fleet. ASEV is a more flexible and more expensive, at $2.6 billion each, substitute for the $1.6 billion Aegis Ashore now operational in Romania and Poland.

Japan’s eight destroyers armed with Aegis anti-missile systems (four Kongos, two Atagos and two Mayas ) and the proposed two ASEVs will give Japan ten Aegis systems, all of them operating from ships. North Korea continues to be a threat and how much more of a ballistic missile threat China becomes is still considered less of a problem now but could escalate in the future. China has a long history of threatening but not acting. North Korea has demonstrated an ability to attack without warning and did so in 2010. North Korea has always been less cooperative than China although the Chinese are still a threat.

What prompted the original Aegis Ashore concept was the Japanese decision, in 2017, that it did not need the more expensive THAAD anti-missile system when it realized that two land-based Aegis systems on the main island could do the same job at less cost. That plus the Aegis equipped destroyers armed with the SM-3A anti-missile missile would enable those two land-based Aegis systems to protect all three of the home islands. Local civilians protested because the missile launches were noisy and the Aegis radar generated a lot of microwave radiation. This forced government officials to oppose the Aegis Ashore and Japan lost the cost savings of a land based system. The expensive ASEV was developed to replace Aegis Ashore.




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