ASEV (Aegis system-equipped vessel) / Aegis Afloat
The "Aegis system-equipped ship" was decided to be introduced as an alternative to the ground-based interceptor missile system "Aegis Ashore". As the study for its construction progressed, it became clear that it had specifications that set it apart from the existing ships currently owned by the Maritime Self-Defense Force. But by early 2023, the government seemed to be backing off from the idea of a 20,000 ton BMD Battlecruiser, leaning towards a rather smaller ship. Regarding the introduction cost, it was estimated that it will be about 480 billion to 500 billion yen [US$3,650,000,000 to US$3,800,000,000] or more for two ships in 2020 money.
The new missile defense policy of 2020 incorporated the construction of two vessels equipped with the Aegis anti-ballistic missile system, as an alternative to the scrapped plan to deploy the land-based Aegis Ashore missile defense system. Defense Minister Kishi Nobuo said Japan must build a robust missile defense system in view of the heightened threats posed by North Korean missiles. Kishi told reporters on Friday that the government will thoroughly consider what kind of equipment will be mounted on the new Aegis vessels and how it should be operated by taking account of the changing situation.
In the areas surrounding Japan, China and Russia deploy a great number of ballistic missiles which can deliver nuclear weapons. Ballistic missile test launches by North Korea have made the threat of ballistic missiles a reality. In order to ensure readiness in response to armed attacks by ballistic missiles and other objects, Japan started developing the BMD system in 2004.
By the end of fiscal year 2010, the Aegis destroyers of the MSDF, “Kongo,” “Chokai,” “Myoko,” and “Kirishima,” completed equipment with BMD capabilities. Regarding the Patriot PAC-3, the ASDF successfully modified a total of 16 fire units of the 1st Air Defense Missile Group (Iruma), the 2nd Air Defense Missile Group (Kasuga), the 4th Air Defense Missile Group (Gifu), the Air Defense Missile Training Group and the 2nd Technical School (Hamamatsu) into PAC-3 capable units.
Concerning Aegis Destroyers, in addition to the existing four “Kongo” class Aegis Destroyers, two “Atago” class Aegis Destroyers were to be equipped with BMD capabilities. Regarding the Patriot PAC-3, one more fire unit of the 5th air defense missile group (Okinawa) will be upgraded into a PAC-3 capable unit. In parallel with the realignment of the existing PAC-3 units, every air defense missile group will have BMD capable PAC-3 fire unit.
The government considered introduce the Terminal High Altitude Area Defense (THAAD) mobile ground-based missile defense system. But Japan would need at least six units to cover the entire country, while Aegis Ashore required just two units. In 2017, Japan decided to deploy two batteries to the Ground Self-Defense Force (GSDF) training areas. Two years later, it chose Akita’s Araya district and Yamaguchi’s Mutsumi for the deployment which was to take place by 2025.
Japan's Defense Minister announced 15 June 2020 the country was cancelling plans to deploy a costly, land-based U.S. missile defense system designed to counter escalating threats from North Korea. Defense Minister Taro Kono told reporters he had decided to "stop the deployment process" of the Aegis Ashore missile system after discovering safety concerns regarding two communities near where the system would be based. Kono said the way the system was currently designed, they could not guarantee that the rocket booster from the missile system would not fall outside the Ground Self-Defense Force's Mutsumi base in Yamaguchi, southwestern Japan.
By 01 August 2020 the Japanese government was considering three main options to replace the halted Aegis Ashore land-based missile shield. A recommendation approved by defense-related panels in the ruling Liberal Democratic Party urges the government to quickly come out with "concrete proposals" to fill the gap left by the absence of the land-based missile shield, which was put on hold last month due to cost concerns.
The three main possibilities were: building a radar system on land that would detect incoming missiles to be shot down by ship-based interceptors, adding more Aegis-equipped ships to the existing fleet, and building a large offshore structure - a megafloat - to house both the radar system and interceptors.
A remote radar system would let the government install the interceptor battery in a location that would minimize the risk of booster rockets falling on residential neighborhoods. Adding more Aegis ships would be expensive to build, and the 600 crew members would be required to staff even two would further strain the chronically understaffed Maritime Self-Defense Force. An artificial island would be vulnerable to threats such as torpedoes and terrorist attacks.
Japan told the United States 06 September 2020 that it viewed building specialized ships to counter ballistic missiles as the most viable alternative to the scrapped plan to deploy land-based, US-developed Aegis Ashore systems. Building vessels equipped with the radar and missile launch system initially destined for Aegis Ashore, whose functions were only limited to countering ballistic missiles, would be cheaper than adding more Aegis-equipped destroyers capable of responding to attacks from fighter jets and submarines as well. The plan emerged as outgoing Prime Minister Shinzo Abe was expected to issue a statement by mid-September to explain the government's stance on missile defense, including the possibility of Japan acquiring a strike capability against missile bases in other countries, as Tokyo sought to review its security policy.
There were several reasons why building specialized ships to counter ballistic missiles was the most viable alternative. The first was trying to fill the shortfall of an arms deal with the US as it canceled the previous plan to deploy Aegis Ashore systems. The plan to build specialized ships would not require local consent, and would curb cancellation fees for Aegis Ashore equipment such as Lockheed Martin Corp.'s SPY-7 radar system, which can be loaded onto the envisioned ships.
Based on US Navy specification for 6.1 m diameter radar, the SPY-7 here might have about 82 RMA's This could translate to about 29 dB loop gain/sensitivity advantage compared to baseline SPY-1 and 3 dB over 69 RMA AMDR. The radar could detect 2m2 RCS target [eg, a missile warhead] at approximately 1,500 km, while something like 10m2 of side aspect of ballistic missile at 2,200 km.
Second, Tokyo hoped to reduce the sensitivity of the project to avoid being criticized by other countries in the Asia-Pacific region. Judging from the name, building specialized ships to counter ballistic missiles seemed to underline the defensive and lowering sensitivity. South Korea's plan to deploy Terminal High Altitude Area Defense in 2017 caused relations with many neighboring countries to deteriorate. Tokyo appeared to have drawn a lesson from Seoul's experience.
Third, the effect of sea-based deployment would be better than land-based. Sea-based deployment to counter ballistic missiles will increase its flexibility to deal with potential attacks. Article 9 of the Japanese Constitution outlaws war as a mean to settle international disputes involving the state. The article requires, Japan to formally renounces the sovereign right of belligerency and aims for international peace based on justice and order. Building specialized ships to counter ballistic missiles does not contravene Article 9 on surface. There have been reports saying the US was considering deploying mid-range missiles on Japanese soil. Such a move will irritate Japan's neighboring countries including China, North Korea and Russia. By contrast, building specialized ships to counter ballistic missiles conveys the idea that Japan was only improving its defensive capability.
And fourth, the sea-based deployment could carry more AEGIS Standard Missile interceptors than the existing DDG missile destroyers, for two reasons. The DDG missile loadout must also include anti-aircraft and anti-ship missiles to account for the destroyers other mission requirements. And the sea-based deployment could carry a larger vertical launch system that the DDG, because it was unconstrained by other design tradeoffs.-
Specialized ships to counter ballistic missiles can be significantly smaller and less expensive than AEGIS destroyers. Japan's national land area of approximately 380,000 km was the 61st place in the world, but the ocean area of the territorial sea + exclusive economic zone (EEZ) covered by resource development rights was actually about 4.47 million km2 and the 6th place in the world, making it abundant minerals on the seabed. The long-cherished desire of Nippon in the Far East was to establish its own energy. The large-scale offshore wind power generation business was becoming the mainstream as a European power generation system that prioritizes environmental issues. Various offshore vessels such as AHTSV (Anchor Handling tug supply vessel) and PSV (Platform supply Vessel), were expected to be introduced in anticipation of future development/scale expansion of offshore business in the territorial waters and exclusive economic zone of Nippon.
Offshore support vessels have high stability/operability even in stormy weather. PSVs were known as the "Sea trucks," as they were used primarily to transport materials and fuel to oil and gas field development rigs. When drilling rigs were transported to different locations, AHTS vessels were used to reel up the anchor from the seabed, tow rigs and support seabed pipeline laying. Both PSV and AHTS were equipped with dynamic positioning systems (DPS) that use the vessel's own propulsion equipment to maintain a fixed position.
A representative AHTS from Kawasaki Kisen Kaisha, Ltd “K” Line was 95 meters long with a breadth of 24 meters and a deadweight displacement of 4,800 Tons.
On 18 December 2020, the Japanese government made a cabinet decision titled "Regarding the development of new missile defense systems and the strengthening of stand-off defense capabilities,"' under which two Aegis-equipped ships were to be built and deployed at sea. It was decided that the Self-Defense Forces would operate it.
Officials had considered the option of special-purpose ships dedicated to intercepting missiles. Such vessels would cost less, but the idea was abandoned since they were vulnerable to submarine or air attacks. These would not be giant destroyers or cruisers, but rather large vessels built to commercial standards with radar and VLS bolted on. Conceptually more like the USN's proposed SABMIS missile defense ship than a super CG. The shps would not inherently require air defense or anti-submarine warfare capabilities, its sole main focus being BMD. This was because North Korea does not currently possess such weapons to attack the ASEV.
Japan considered using a large ship as an alternative to the Aegis Ashore missile defense system. Kyodo News reported 01 November 2020 that the Defense Ministry was considering a 9,000-ton [light displacement] ship to mount the new Aegis system, allocating larger living space for crew. If realized, it would be the largest Aegis-equipped vessel of the Maritime Self-Defense Force. The larger ship wsa needed because the new SPY-7 radar's height required a vessel beam greater than that of the conventional Aegis destroyers.
The proposed 9,000 ton light displacement [probably 11,000 tons full loaded] exceeded that of the Maya, the largest Aegis destroyer, with a light displacement of 8,200 tons [full displacement of 10,000 tons]. Some sources suggested that possibly a final pair of hulls could be completed to the revised specification including AN/SPY-7 radars, but adding beam to the hull might pose a challenge.
In June 2020 the government cancelled plans to deploy the shore-based anti-missile complexes, saying the deployment in the prefectures of Akita and Yamaguchi would put residents at risk of falling rocket boosters. The ministry also said that modifying the technology would take years and cost too much.
As a substitute measure, the ministry focused on two possible options -- remodeling private-sector vessels to mount the Aegis system and building dedicated maritime ships with the system. The decision would be made around the end of 2020 after the ministry received an interim report in mid-November from two private firms studying with the issue.
In July 2021 it was reported that the Defense Ministry plans to use Lockheed Martin Corp.’s SPY-7 radar system for its planned Aegis-equipped vessels, though the system was intended for use on land. The Aegis ships will be built as an alternative to the Aegis Ashore ground-based ballistic missile defense system,
The original idea for this ship was a SWATH or catamaran hull for better stability. Thoae concepts did not really look like traditional warships, more just radar platforms with some VLS strapped on. Then ideas focused on SPY-7 monohull ships, less cruiser, more fleet auxiliary with a very large radar. However, reports that the new ships will also carry Type 12 cruise missiles could imply that that want a more conventional all-around warship. A large surface combatant based on an Izumo hull could cover more than BMD with the Type 12 ASCM. The speed of the Izumo hull would also give it the ability to keep up with the rest of the fleet while the LPD hull would slow it down by almost 10 kts.
By late 2022 Japan had plans to construct its largest warship since the Second World War for the purpose of anti-ballistic missile interception. These planned ships were not Destroyers, but rather Aegis ships. Both were sometimes recognized as having the same meaning, but in Japan, the two were distinct concepts. Land-based Aegis was planned, but the plan was canceled due to opposition from the residents of the planned construction site. This was the alternative, and in order to carry the equipment that was supposed to be on land, the ship inevitably became huge. The massive scale of the vessels will lend it stability under heavy sea states, increasing interception readiness, and increase endurance at sea, similarly increasing combat readiness. Some believe that the hull was enlarged to solve the problem of the size and weight of the SPY-7, a radar manufactured by Lockheed Martin that will be installed on the ASEV. The largest vessel in the JMSDF would be more like a civilian vessel than a warship in that all crew members were given private cabins and the crew complement was quite low for a vessel of this size.
On 17 August 2022 Yomiuri Shimbun reported that to increase deterrence against North Korea’s missiles, the government plans to place domestic long-range cruise missiles on two naval vessels equipped with the Aegis system it plans to build. These missiles were capable of striking land-based targets as the ships will be designed on the expectation that the vessels have “counterattack capability” such as to destroy an enemy’s missile launch site in the name of self-defense. To keep down construction costs, it had also been settled that the ships will be built using a typical single hull, according to several government sources. In addition to the advanced radar and missiles, the Aegis system-equipped ships were likely to carry cruise missiles that will be upgraded versions of the Type 12 surface-to-ship missile currently used by the Ground Self-Defense Force. After the upgrades, the missile’s range will extend to about 1,000 kilometers and it will be mounted on naval vessels.
Regarding the technical specifications of the ships, nothing was mentioned. Initial details of the ASEV point towards a massive ship: 690 feet / 210 meters long and 130 feet / 40 meters beam, with a standard displacement of 20,000 tons [full displacement closer to 25,000 tons] and a crew of about 110 people. Crew comfort onboard will be a priority as all crew members will be provided with private cabins. In terms of length and displacement, it was equivalent to the Izumo class DDH (248 meters long, standard displacement 19,500 tons), the largest vessel in the JMSDF.
Last but not least, the document gave a target of commissionning for the two destroyers. Indeed, the MoD had the ambition to get them by FY2027, meaning between April 2027 and March 2028. This time was necessary in order to develop the J7.B Aegis Weapon System (AWS) system that will fit on those vessels. According to Lockheed Martin, J7.B was the integration of SPY-7 radar into J7 (BL9), the latest software currently installed by JMSDF’s Aegis ships. For the record, the J7.B system had been successfully tested in August 2022 by the Missile Defense Agency (MDA) in front of the JMSDF.
Japan was considering downsizing two destroyers to be built with the Aegis ballistic missile interceptor system from their original design in a bid to increase their mobility, government sources said 09 November 2022. Now they will be scaled down to nearly on par with the 8,200-ton Maya, the nation's biggest Aegis-equipped vessel. The ministry also aimrd to use Lockheed Martin Corp.'s SPY-7 radar, which was supposed to be used for the land-based Aegis Ashore system, on the new destroyers while adding the ability for them to respond to hypersonic glide weapons,
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