Aegis system equipped vessels (ASEV)

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 s, with the combined main deck area sufficient to accommodate the Aegis radar deckhouse and battery of SM-6 interceptor missile launchers. Current design Original plans for the two ASEV ships called for a cruiser-sized warship with a standard displacement of each, an overall length of , and a beam of 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." 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). 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). 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. Given the manpower requirements, non-BMD armament may be limited to such close-in self-defense weapon systems as Phalanx CIWS or SeaRAM. 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 ; 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 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 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 s 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 and helicopter carriers as well as s. 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 s. 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 ASEV 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. ==Ships in the class==

Naming conventions Neither ASEV warship has been officially named. Ships of the JMSDF are known as Japan Ships (; Go'[e]i:-Kan; prefix JS) and are classified according to the warship type. ASEV warship will be designated as a guided-missile cruiser (CG), but it is not known if they will be named after provinces, like the Helicopter Destroyers (DDH) and Multipurpose Carriers (CVM), or after mountains, like the Guided Missle Destroyers (DDG) ==See also==