# Aegis system equipped vessels (ASEV)

Aegis system equipped vessels (ASEV) or (Japanese: イージス・システム搭載艦) are a pair of ballistic missile defense (BMD) warships under construction to be operated by the Japanese Maritime Self-Defense Force (JMSDF) as dedicated sea-based BMD platforms, serving as an alternative to Japan's now-cancelled land-based Aegis Ashore BMD system.

## Background

Two East Asian nations have nuclear weapons and the means to delivery such weapons—the People's Republic of China (PRC) and the Democratic People's Republic of Korea (DPRK) or North Korea. The range of PRC and DPRK missiles are illustrated below.

### Chinese and North Korean missile ranges

* Chinese Conventional Strike Ranges as of 2020
* Chinese Nuclear Ballistic Missile Strike Ranges as of 2020
* Estimated range of North Korean missiles as of 2015

### People's Republic of China

The first of China's nuclear weapons tests took place in 1964, and its first hydrogen bomb test occurred in 1967. Tests continued until 1996, when China signed the Comprehensive Test Ban Treaty (CTBT) although the PRC is not a signatory of any multilateral nuclear arms limitation or reduction treaties. The People's Liberation Army Rocket Force (PLARF; Chinese: 中国人民解放军火箭军; pinyin: Zhōngguó Rénmín Jiěfàngjūn Huǒjiàn Jūn) controls China's arsenal of land-based ballistic missiles—both nuclear and conventional. The armed service branch was established on 1 July 1966 and made its first public appearance on 1 October 1984. The headquarters for operations is located at Qinghe, Beijing. The PLARF is under the direct command of the Chinese Communist Party's Central Military Commission (CMC). The People's Liberation Army Navy Submarine Force (PLANSF) is the submarine service of the People's Liberation Army Navy (PLAN) and controls submarine-launched ballistic missile forces of the PRC.
In an online article dated 13 January 2023, research associate Timothy Wright of the International Institute of Strategic Studies (IISS) wrote that PRC has "significantly" boosted its strategic nuclear capabilities with ongoing upgrades to its submarine-launched and land-based nuclear forces, noting recent confirmation from recent official statements and published analysis from the U.S. Department of Defense. The article also stated that the DoD raised its estimates of ICBM missile silos from 100 in 2022 to 300 in 2022 based on current trends. The DoD also estimated that the PRC had over 400 "operational" nuclear warheads in its inventory as of 2022 and could reach 1,500 by 2035.

### Democratic People's Republic of Korea

North Korea showed an interest in developing nuclear weapons dating back to the 1950s. The nuclear program can be traced back to about 1962, when North Korea committed itself to what it called "all-fortressization", which was the beginning of the hyper-militarized North Korea of today. In 1963, North Korea asked the Soviet Union for help in developing nuclear weapons, but was refused. The Soviet Union agreed to help North Korea develop a peaceful nuclear energy program, including the training of nuclear scientists. Later, China, after its nuclear tests, similarly rejected North Korean requests for help with developing nuclear weapons. The Korean People's Army Strategic Force (Korean: 조선인민군 전략군), is the military branch of the Korean People's Army that oversees North Korea's nuclear and conventional strategic missiles. It is mainly armed with surface-to-surface missiles of domestic design as well as older Soviet and Chinese models. The KPA Strategic Force was established in 1999 when several missile units under KPA Ground Force Artillery Command were re-organized into a single missile force reporting directly to the office of the Supreme Commander of the KPA via the General Staff.
As of early 2020, North Korea's nuclear arsenal is estimated approximately 30 to 40 nuclear weapons and sufficient production of fissile material for six to seven nuclear weapons per year. North Korea has also stockpiled a significant quantity of chemical and biological weapons. In 2003, North Korea withdrew from the Treaty on the Non-Proliferation of Nuclear Weapons (NPT). Since 2006, the country has been conducting a series of nuclear weapon tests at increasing levels of expertise and frequency, prompting the imposition of sanctions. More recently, on September 9, 2022, North Korea passed a law to declare itself a nuclear weapons state and rejected any possibility of denuclearisation. In December 2022, North Korea ground-tested a solid-propellant rocket motor for potential use on either a land-based or submarine-launched Intercontinental ballistic missile (ICBM).
As of 20 March 2020, North Korea has carried out 147 tests of strategic missiles since its first such test in 1984. 15 were carried out under the rule of Kim Il Sung and 16 under Kim Jong Il. Under Kim Jong Un, 119 tests have been undertaken as of December, 2019. An additional 8 missiles in 2021 and 63 in 2022 were subsequently launched (See bar chart below.), and a total of 7 North Korean missiles flew over the Japanese archipelago since 1998 (See table below, and the map and graph on the right.).
In its published overview for the Fiscal Year 2023 budget, the Japanese Ministry of Defense (MOD) noted that nine ballistic missiles were launched on 4 August 2022 alone, with five landing within Japan's exclusive economic zone (EEZ) while also noting the DPRK's new "hypersonic" Hwasong-17 ballistic missile system. On 3 November 2022, North Korea reportedly fired at least one ballistic missile off its east coast, including one believed to be a long-range missile, that flew over and past Japan. The launch triggered the Japanese emergency broadcast system, which alerted residents in the prefectures of Miyagi, Yamagata, and Niigata to stay indoors. Later, on 18 November 18, 2022, North Korea reportedly fired at least one ballistic missile into the sea on Friday, believed to be the first successful full flight of its Hwasong-17. The missile landed in Japan's exclusive economic zone.
Through the end of March, North Korea has launched a combination of at least 2 long-range and 11 short-range ballistic missiles, as well as multiple cruise missile firings, in 2023 thus far, with the Hwasong-15 ICBM launched on 18 February 2023 travelling for approximately 989 kilometres (615 mi) at a "lofted angle" before landing in the sea just west of Japan. On 13 April 2023, North Korea launched an additional missile, while residents of Hokkaido were told to seek immediate shelter following statements by Kim Jong-Un wherein he called for "more practical and offensive" capabilities.
On 19 November 2023, ROK Defense Minister Shin Won-sik informed the Korean Broadcasting System that an anticipated third satellite launch by North Korea was expected by the end of that month. On the evening of 21 November 2023, North Korea's state-run Korean Central News Agency (KCNA) reported that a Chŏllima 1 rocket carrying a Malligyong-1 reconnaissance satellite was launched from the Sohae Satellite Launching Station, with North Korean leader Kim Jong Un present. On 23 November 2023, North Korea terminated the bi-lateral 2018 Comprehensive Military Agreement in response to South Korea's decision to suspend a part of that agreement in reaction to North Korea's latest satellite launch.
On 18 December 2023, South Korea said North Korea has fired its most advanced intercontinental ballistic missile. The launch came a week after South Korean and U.S. defense officials met to update plans on how to respond to a nuclear attack from the North. South Korean and Japanese officials said the missile travelled for 73 minutes, covering about 1,000 km (621 miles).
North Korean rockets flown over the Japanese archipelago :
| No. | Date | Model | Area flown over | Advance notice | North Korean claim | Satellite name |
| 1 | August 31, 1998 | Taepodong-1 | Akita | No | Satellite launch | Kwangmyŏngsŏng-1 |
| 2 | April 5, 2009 | Unha-2 | Akita, Iwate | Yes | Satellite launch | Kwangmyŏngsŏng-2 |
| 3 | December 12, 2012 | Unha-3 | Okinawa | Yes | Satellite launch | Kwangmyŏngsŏng-3 |
| 4 | February 7, 2016 | Kwangmyŏngsŏng (Unha-3) | Okinawa | Yes | Satellite launch | Kwangmyŏngsŏng-4 |
| 5 | August 29, 2017 | Hwasong-12 | Hokkaido | No | Missile launch | N/A |
| 6 | September 15, 2017 | Hwasong-12 | Hokkaido | No | Missile launch | N/A |
| 7 | October 4, 2022 | Hwasong-12 (presumed) | Aomori | No | | |
Note: Text, table, and graphics copied from List of North Korean missile tests; see that page's history for attribution.

### Japanese Aegis Ashore program

Japan began developing its current ballistic missile (BDM) system starting in 2004. On 19 December 2017, the Cabinet of Japan approved a plan to purchase two Aegis Ashore systems equipped with the AN/SPY-7(V)1, based on Lockheed Martin's Long Range Discrimination Radar (LRDR) to increase Japan's self-defence capability against North Korea, using SM-3 Block IIA missiles, and also could work with SM-6 interceptors capable of shooting down cruise missiles. The installation sites are at a Ground Self-Defense Force training area in Araya District, Akita Prefecture and the Mutsumi training area in Hagi, Yamaguchi Prefecture (See Map, Red: BMD FPS-5 radar, Yellow: BMD FPS-3 Kai radar, Blue: Air Defense Group, Anchor: JMSDF Aegis destroyers).
* Initial locations of major JSDF BMD installations (2020)
* U.S. Pacific Missile Range Facility
* NATO's AABMDS site in Deveselu, Romania
* NATO's AABMDS site in Redzikowo, Poland
The proposed Japanese Aegis Ashore program would have been comparable to the land-based Aegis Ashore Ballistic Missile Defense System (AABMDS) sites deployed by the U.S. in Romania (pictured) and Poland (pictured). Test installation was built at the U.S. Pacific Missile Range Facility in Hawaii (pictured) in the 2000s. A site in Deveselu, Romania is operational since 2016, while a site at Redzikowo, Poland was slated to become operational in 2022.
On 30 July 2018, Japan picked Lockheed Martin Corp to build a US$1.2 billion radar for two ground-based Aegis ballistic missile defense stations. These are meant to guard against missile strikes. On the same day, Japan's Defense Ministry considered to withdrawing PAC-3 missile interceptor units from the country's northern and western region amid an easing of tensions with North Korea. Ministry officials noted that North Korea is less likely to fire ballistic missiles after it held a summit with the United States on the previous month. But the officials also said the ministry will maintain its order to destroy any incoming missiles. They added that the ministry will be ready to quickly redeploy the PAC-3 units if the situation changes.
Japan's Foreign Minister Hirofumi Nakasone and South Korea's Minister of Foreign Affairs Yu Myung-hwan agreed that the launch of the North Korean Unha-2 satellite on April 5, 2009, violated United Nations resolutions 1695 and 1718, both adopted in 2006. Japan's cabinet examined approval of a JMSDF AEGIS BMD engagement in the event of a failure of the Taepondong launch. The Japanese government also noted that it could bypass the Japanese Cabinet for an interception under Article 82, Section 2, Paragraph 3 of the Self-Defence Forces law. In total, five AEGIS destroyers were deployed at that time. Supplemental to SM-3 capability the Japanese system incorporates an airborne component. Together discrimination between platform tests and satellite launches is possible by analyzing the angle of ascent.
On 15 June 2020, Japanese Defense Minister Taro Kono announced that work had been halted on the deployment of the Aegis Ashore system because additional costs would be needed to ensure that residential buildings would not be hit by rocket boosters used to launch the missiles. Later in the month Japan's National Security Council confirmed the cancellation of Aegis Ashore. On 23 September 2020, Lockheed Martin noted the potential expense to convert the anti-aircraft (AA) system for maritime use since a revamp in the design is required. The JMSDF has equipped four ships of the Kongo-class destroyers for Long-Range Surveillance Team (LRST) and engagement — JS Kongo, JS Chokai, JS Myoko, and JS Kirishima.

### JMSDF Aegis Afloat

The JMSDF currently operates 4 Kongō class, 2 Atago class, and 2 Maya class guided-missile destroyers as part of its "Aegis Afloat" program (See table below.).
On 6 October 2022, five warships from the United States, Japan, and South Korea held a multilateral ballistic missile defense exercise in the Sea of Japan (pictured) as part of the military response to ongoing North Korean intermediate-range ballistic missile tests over the Japanese home islands.
On 16 November 2022, the guided-missile destroyer Maya fired an SM-3 Block IIA missile, successfully intercepting the target outside the atmosphere in the first launch of the missile from a Japanese warship. Two days later, the Haguro likewise fired an SM-3 Block IB missile with a successful hit outside the atmosphere. Both test firings were conducted at the U.S. Pacific Missile Range Facility on Kauai Island, Hawaii, in cooperation with the U.S. Navy and U.S. Missile Defense Agency. This was the first time the two ships conducted SM-3 firings in the same time period, and the tests validated the ballistic missile defense capabilities of Japan's newest Maya-class destroyers.
On 22 February 2023, five warships from the United States, Japan, and South Korea held a multilateral ballistic missile defense exercise in the Sea of Japan in response to the launch of a North Korean Hwasong-15 ballistic missile on 18 February 2023, landing in Japan's exclusive economic zone (EEZ) in the Sea of Japan, in an area 125 miles west of the island of Ōshima, which lies 30 miles (48 km) west of the main island of Hokkaido. Two additional IBCBMs were subsequently launched on 20 February 2023, with both landing in the Sea of Japan off the east coast of the Korean Peninsula. On 19 December 2023, United States, Japan, and South Korea announced the activation of a real-time North Korea missile warning system as well as jointly established a multi-year trilateral exercise plan in response to North Korea's continued ballistic missile launches.

#### List of Aegis Afloat ships

| Name | Hull Pennant No. | Builder/Shipyard | Aegis Radar | Anti-Ballistic Missile | Vertical Launchers | Commissiomed | Home port | Flotilla | Squadron | Status |
| Maya class |||||||||||
| JS Maya | DDG-179 | JMU, Yokohama | AN/SPY-1D(V) | SM-3 Standard missile | Mark 41: 96 cells (total) | 19 March 2020 | Yokosuka | Escort Flotilla 1 | Escort Squadron 1 | Active |
| JS Haguro | DDG-180 | JMU, Yokohama | AN/SPY-1D(V) | SM-3 Standard missile | Mark 41: 96 cells (total) | 19 March 2021 | Sasebo | Escort Flotilla 4 | Escort Squadron 8 | Active |
| Atago class |||||||||||
| JDS Atago | DDG-177 | JMU, Yokohama | AN/SPY-1D(V) | SM-3 Standard missile | Mark 41: 96 cells (total) | 15 March 2007 | Maizuru | Escort Flotilla 3 | Escort Squadron 3 | Active |
| JDS Ashigara | DDG-178 | JMU, Yokohama | AN/SPY-1D(V) | SM-3 Standard missile | Mark 41: 96 cells (total) | 13 March 2008 | Sasebo | Escort Flotilla 2 | Escort Squadron 2 | Active |
| Kongō class |||||||||||
| JDS Kongō | DDG-173 | Mitsubishi Heavy Industries | AN/SPY-1D PESA | SM-3 Standard missile | Mark 41: 90 cells (total) | 25 March 1993 | Sasebo | Escort Flotilla 1 | Escort Squadron 5: | Active |
| JDS Kirishima | DDG-174 | Mitsubishi Heavy Industries | AN/SPY-1D PESA | SM-3 Standard missile | Mark 41: 90 cells (total) | 16 March 1995 | Yokosuka | Escort Flotilla 2 | Escort Squadron 6 | Active |
| JDS Myōkō | DDG-175 | Mitsubishi Heavy Industries | AN/SPY-1D PESA | SM-3 Standard missile | Mark 41: 90 cells (total) | 14 March 1996 | Maizuru | Escort Flotilla 3 | Escort Squadron 3 | Active |
| JDS Chōkai | DDG-176 | IHI Corporation | AN/SPY-1D PESA | SM-3 Standard missile | Mark 41: 90 cells (total) | 20 March 1998 | Sasebo | Escort Flotilla 4 | Escort Squadron 8 | Active |

## Design

In 2020, Japanese Defense Minister Nobuo Kishi announced plans to build 2 new Aegis destroyers to replace its scrapped land-based Aegis Ashore ballistic missile interceptors program. On August 31, 2022, the Japan Ministry of Defense announced that JMSDF will operate two "Aegis system equipped ships" (イージス・システム搭載艦 in Japanese) to replace its earlier cancellation of the Aegis Ashore program, commissioning one ship by the end of fiscal year 2027, and the other by the end of FY2028. The budget for design and other related expenses are to be submitted in the form of “item requests” (i.e., engine components), without specific amounts, and the initial procurement of the lead items are expected to clear legislation by FY2023. Construction is to begin in the following year of FY2024. The overall cost of building both ships is estimated to be 1 trillion yen (US$7.1 billion). The first ship is planned to be commissioned in 2028 and the second in 2029.

### Initial SWATH design approach

Preliminary design postulated that the ASEV would be based on the Small Waterplane Area Twin Hull (SWATH) configuration used by Hibiki-class ocean surveillance ships, with the combined main deck area sufficient to accommodate the Aegis radar deckhouse and battery of SM-6 interceptor missile launchers. Such a SWATH-based configuration would be comparable to the 1986 CGH-67 design study (pictured) by the then David W. Taylor Naval Ship Research and Development Center of the U.S. Navy's Naval Sea Systems Command (NAVSEA) albeit without the explicit BMD orientation.

### Current design

Original plans for the two ASEV ships called for a cruiser-sized warship with a standard displacement of 20,000 long tons (20,000 t) each, an overall length of 690 ft (210 m), and a beam of 130 ft (40 m) on a monohull configuration. The overall size offers enhanced habitability for its 110-person crew for extended deployments and relative simplicity in construction, and it is designed to provide a stable platform for its advanced sensors and weapon systems. Once completed, the two warships will be the largest surface combatant ships in service with the JMSDF, and according to Popular Mechanics, they will "arguably [be] the largest deployable surface warships in the world."
However, in November 2022, both Kyodo News and Jiji Press quoted an unnamed senior official in Japan's Ministry of Defense who noted that the proposed ASEV warships might be downsized in a size similar to Maya-class destroyers as their original proposed beam significantly reduced speed and maneuverability, making the ships easier to detect and target by the enemy. Later, on 23 December 2022, the Japanese MOD released additional 2023 budget and program guidance, including the first official illustration of the ASEV warship (See article info-box.), although no further details on ASEV ship dimensions were provided beyond the original facts and figures from the August 2022 release. USNI news editor Sam LaGrone noted that the overall design of the ASEV warship was comparable to the U.S. Navy's next-generation DDG(X) guided-missile destroyer (pictured).

### Procurement

According to its published budget overview, for Fiscal Year 2023, the Japanese Ministry of Defense allocated 22.8 billion yens (US$1.654 billion) for the initial procurement of advanced components for the ASEV program in order to "significantly improved BMD capability capable of responding to lofted and simultaneous ballistic missiles, as well as expandability for responding to HGVs and other such threats." In related news, in a statement released on April 4, 2023, the Japanese Ministry of Defense announced the signing of four contracts worth 382.47 billion yens (US$2.83 billion) last week with Mitsubishi Heavy Industries (MHI) for development of standoff defense weapon systems for the Japanese Self Defense Force (JSDF). This standoff defense capability is expected to provide the JSDF with long-range strike capabilities against ships and amphibious forces invading Japan, particularly at its remote islands, such as the disputed Senkaku Islands administered by Japan, and its southwestern islands.
On 19 December 2023, Defense Minister Minoru Kihara announced approval for the funding for the construction of Aegis System Equipped Vessels (ASEV) in Fiscal Year 2024 and FY 2025 to be commissioned in 2027 and 2028 respectively. Initial FY 2024 ASEV funding was set at 373.1 billion yen (US$2.6 billion), a slight reduction from the 379.7 billion yen (US $2.64 billion) that the Japanese Ministry of Defense had sought in its initial FY 2024 budget request submitted in August 2023. This ASEV procurement decision was subsequently affirmed when the Japanese Cabinet approved the Ministry of Defense's budget for Fiscal Year 2024 on 22 December 2023.

## Equipment
### Ballistic missile defense systems

As a ship-based alternative to the land-based Aegis Ashore system, the Aegis system-equipped warships could be armed with the Standard Missile 6 (SM-6) Sea-Based Terminal (SBT) system (pictured), as well as the J7.B Aegis Weapon System and Lockheed Martin's SPY-7(V)1 multi-functional radar, initially contracted for Aegis Ashore. According to Lockheed Martin, J7.B is the integration of SPY-7 into J7 (BL9), the latest software currently installed on JMSDF's Aegis-equipped guided missile destroyers. The SPY-7(V)1 radar uses scaled equipment and software derived from the advanced Long Range Discrimination Radar (LRDR) located in the Clear Space Force Station, Alaska, and operated by the U.S. Missile Defense Agency (MDA).
In support of this objective, on 20 October 2022, the U.S. Department of State approved and the Defense Security Cooperation Agency (DSCA) notified the United States Congress that Japan is set to be the first country after the United States to field the Standard Missile 6 (SM-6) as part of a proposed US$450 million Foreign Military Sale (FMS) arms package. Pending Congressional approval, Japan was conditionally approved to buy up to 32 of the Raytheon-built SM-6 Block I missiles. This notification is a follow-up of a 2017 decision from U.S. Department of Defense that conditionally approved Japan, South Korea, and Australia to buy SM-6 missile systems.

### Weapon systems

The ASEV warships will be equipped to defend against hypersonic glide vehicles, as such new hypersonic missile designs are too evasive for current ballistic missile defense systems to reliably intercept. Also, the two ships will be equipped with the upgraded sea-based version of the Type-12 anti-ship cruise missile (ASCM) system capable of striking land and naval targets with a range of around 1,000 km (540 nmi; 621 mi). Given the manpower requirements, non-BMD armament may be limited to such close-in self-defense weapon systems as Phalanx CIWS or SeaRAM.
On 16 December 2022, Defense Buildup Program (防衛力整備計画) document announced a 110.4 billion yen (US$820 million) budget allocation to modify the JMSDF's Aegis-equipped guided missiles destroyers to carry Tomahawk land attack cruise missiles (TLAM). Although it is not stated what specific modifications are to be undertaken, Lockheed Martin's Tactical Tomahawk Weapons Control System (TTWCS) is the likeliest system to be integrated into the Aegis destroyers. The Japanese government had previously approached the U.S. government to purchase the U.S.-made Tomahawk cruise missile for attacking enemy bases. The Japanese government decided to purchase the Tomahawk cruise missile before their domestically built improved range Type 12 surface-to-ship missile systems started full-scale operation. The intent behind the JMSDF acquiring both long-range cruise missile systems is to act as a deterrent to North Korea, with the weapons able to strike naval and land targets.
In a tweet posted on 17 December 2022, Satō Masahisa, Director, Committee on Foreign Affairs and Defense of the House of Councillors in the Diet, stated that the proposed ASEV warships would be capable of speeds in excess of 30 knots (56 km/h); Standard Missile 6 (SM6) and Evolved SeaSparrow Missile (ESSM) systems; 12 anti-ship standoff missiles; Cooperative Engagement Capability (CEC) and Engage-on-Remote (EoR) functions; and now 128 VLS cells. On 23 December 2022, the Japanese Ministry of Defense released its 2023 budget and program guidance that featured the first official illustration of the ASEV warship, revealing that its missile arsenal will use the Mark 41 Vertical Launching System (Mk 41 VLS) grouped in two locations, forward of the bridge deckhouse and aft above the helicopter hangar.
On 17 November 2023, the U.S. Department of State announced the sale of up to 200 Tomahawk Block IV All Up Rounds (AURs) (RGM-109E) cruise missiles, 200 Tomahawk Block V AURs (RGM-109E) cruise missiles, and 14 Tactical Tomahawk Weapon Control Systems to the Japanese Ministry of Defense as part of a part of a US$2.35 billion foreign military sales package. One month previously Japanese Defense Minister Minoru Kihara indicated a planned buy of Block IV Tomahawks in FY2025 and Block V in FY2026 and FY2027, thereby advancing acquisition Block IV acquisition by a year. In a press conference on 20 November 2023, Kihara stated that the Defense Ministry would coordinate closely with United States in the delivery of the Tomahawk missile system on its sea-based and ground platforms. On 28 March 2024, the Japanese Ministry of Defense announced the start of Tomahawk missile training of JMSDF personnel by the United States Navy. Initial training would take place onboard the guided-missile destroyer USS McCampbell (DDG-85) based at United States Fleet Activities Yokosuka.

### Ship sensor systems

The ASEV warships will use the UNIted COmbined Radio aNtenna (UNICORN) NORA-50 integration mast, which has a bar-shaped dome that houses the antennas for tactical data link, Tactical Air Navigation System (TACAN), and communications. According to the Acquisition, Technology & Logistics Agency (ATLA), UNICORN has a shape designed to reduce the radar cross section (RCS), which makes it stealthy. It is currently being installed on the Mogami-class frigates entering service or under construction, and there is a possibility that they will be considered for integration into the proposed Next-Generation Offshore Patrol Vessel program.

### Propulsion & power systems

Given the manning and electrical requirements, the Aegis system equipped vessels (ASEV) requires a highly automated, low maintenance, all-electrical propulsion system. One such system is a Combined diesel and gas (CODAG) propulsion (pictured), consisting of diesel engines for cruising and gas turbines that can be switched on for high-speed transits, and it is used on the JMSDF's Hyūga class and Izumo class helicopter carriers as well as Mogami-class frigates. In May 2024, it was announced that the two ASEV warship would be equipped with Rolls-Royce MT30 gas turbines as their main propulsion plant.

## Operational concept

On 16 December 2022, the Japanese Cabinet approved a trio of defense-related policy documents, including its new National Security Strategy (NSS or 国家安全保障戦略), the strategic guideline document for the Japanese government's policies regarding diplomacy, defense, and economic security for the next decade. Based on the NSS, the National Defense Strategy (NDS or 国家防衛戦略) document outlined Japan's defense policy goals and the means to achieve them while the Defense Buildup Program (DBP or 防衛力整備計画) document outlined the scale of the introduction of specific defense equipment within the budgetary objectives. According to the Defense Buildup Program document, the JMSDF will increase the number of Aegis-equipped guided-missile destroyers (DDG) from the current 8 to 10 warships, as well as the introduction of two Aegis system-equipped vessels (ASEV) to be deployed in ballistic missile defense (BMD) operations. By the end of the decade, the JMSDF will operate 12 ships equipped with Aegis Weapon System (AWS) and likewise plans to replace its fleet of older, less capable destroyers and destroyer escorts with Mogami-class frigates.
On 23 December 2022, the Japanese Ministry of Defense's 2023 budget and program guidance documented provided examples of operations (運用の一例) for the Aegis-equipped naval forces of the Japanese Maritime Self Defense Force (MSDF). The two ASEV warship would be exclusively tasked for dedicated ballistic missile defense (BDM) missions (BMD等) and operate off the Korean peninsula in the Sea of Japan, allowing the other Aegis guided-missile destroyers to meet other contingencies (侵攻阻止) while operating independently to maintain the maritime domain awareness (MDA) and keep the sea lines of communication (SLOC) open in the East China Sea southwest of the Japanese home islands (pictured).

## Criticisms

Senior research fellow Brent Sadler of The Heritage Foundation criticized the proposed ASEV program, noting that the total of two units was insufficient to keep an AESV ship deployed continuously at sea. Sadler noted that the more typical operational cycle would require at least three ships, with one ship at sea on deployment, a second ship undergoing refit and upkeep following deployment, and a third ship going through work-up for deployment to relieve the first ship. Sadler also noted that the 2027–2029 timeframe to complete the construction of both AESV ships leaves Japan highly vulnerable during the interim period. Regarding Japan's relative vulnerability, StrategyPage noted that the original Aegis Ashore BMD land-based facilities would not have been operational until 2024.
Additionally, senior defense analyst Felix Chang of the Foreign Policy Research Institute (FPRI) observed that the proposed ASEV warships would be extremely vulnerable to such next-generation Chinese anti-ship ballistic missiles as the DF-21D and DF-26, with DF-21D having a range of 1,500 kilometers while the DF-26 has a range of 4,000 kilometers. Chang also mentioned that China has fitted its DF-21D missiles with maneuverable reentry vehicles that guide with terminal seekers to compensate and correct for any inaccurate targeting data.
Finally, senior fellow Zack Cooper of the American Enterprise Institute pointed out that a sea-based BMD system is overall not a more cost-effective alternative to a shore-based system. In 2020, Japanese news media reported that officials within the Japanese Ministry of Defense recognized that alternatives to the land-based Aegis Ashore system would all be significantly more expensive, by up to half again as costly.

## Ships in the class

| Building No. | Name | Hull Pennant No. | Builder/Shipyard | Plan | Laid down | Launched | Commissioned | Home port | Flotilla | Squadron | Status | Note |
| TBD | Unit 1 | TBD | Mitsubishi Heavy Industries (MHI) | 2023 | 2024 (est.) | TBD | 2027 (est.) | TBD | TBD | TBD | Authorized | |
| TBD | Unit 2 | TBD | Japan Marine United (JMU) | 2023 | TBD | TBS | 2028 (est.) | TBD | TBD | TBD | Authorized | |

### Naming conventions

Neither ASEV warship has been officially named. Ships of the JMSDF are known as Japan Ships (護衛艦; Go'[e]i:-Kan) and are classified according to the warship type. Guided-missile destroyers (DDG) are named after the names of places in Japan, such as mountains and provinces while more conventional destroyers (DD) are named after natural phenomena in the heavens or the atmosphere as well as mountains, rivers or regions. It is not known if ASEV warship will have a new type designation such as guided-missile cruiser (CG) or ballistic missile defense ship (BMD Ship).