Aegis system-equipped vessels

• December 19, 2023, Defence Minister Minoru Kihara confirmed the approval of funding
• The Aegis system-equipped vessels (ASEV) represent a significant advancement in Japan's maritime defence capabilities
• This reconsideration follows concerns that the initially proposed beam would impair speed and manoeuvrability

The Aegis system-equipped vessels (ASEV) represent a significant advancement in Japan's maritime defence capabilities, as they are being constructed to serve as specialised ballistic missile defence (BMD) warships for the Japan Maritime Self-Defence Force (JMSDF). These sophisticated vessels are designed to replace the now-cancelled land-based Aegis Ashore BMD system, reflecting a strategic shift towards enhanced sea-based defence mechanisms.

According to the Ministry of Defence (MoD), the ASEV boasts impressive dimensions, measuring approximately 190 meters in length and twenty-five meters in width. With a standard displacement of around 12,000 tons, these vessels are engineered to accommodate advanced weaponry and system technologies crucial for effective missile interception. In scenarios demanding full operational capacity, the total displacement is expected to exceed 14,000 tons, showcasing the vessel's robust design for diverse operational demands.

Design

In 2020, Japanese Defence Minister Nobuo Kishi announced the intention to construct two new Aegis destroyers to succeed the discontinued land-based Aegis Ashore ballistic missile interceptor program. On August 31, 2022, the Japanese Ministry of Defence confirmed that the Japan Maritime Self-Defence Force (JMSDF) would operate two "Aegis system-equipped ships" as a replacement for the Aegis Ashore program. The Ministry plans to commission one vessel by the end of fiscal year 2027, with the second vessel scheduled for commissioning by the conclusion of fiscal year 2028. The budget for design and other associated costs will be submitted in the form of “item requests,” which will include specific components such as engine parts, without disclosing precise amounts. It is anticipated that the initial procurement of key items will receive legislative approval by FY2023. Construction is projected to commence the following year, FY2024. The estimated overall expenditure for the construction of both ships is approximately one trillion yen (equivalent to US$7.1 billion). The first ship is slated for commissioning in 2028, while the second is expected to be commissioned in 2029.

Consistent with all Japanese Aegis destroyers, these vessels will feature three AN/SPG-62 X-band radar illuminators, which are responsible for designating targets for final interception by air defence missiles that primarily utilise semi-active radar homing technology. Additionally, the ship's mast will accommodate the AN/SPQ-9B radar, which provides horizon-range scanning capabilities and is capable of automatically detecting and tracking low-flying anti-ship cruise missiles (ASCMs), surface threats, as well as low-speed aircraft, unmanned aerial vehicles (UAVs), and helicopters simultaneously. Moreover, this model will incorporate the Advanced Surface Electronic Warfare Improvement Program (SEWIP) Block 2 AN/SLQ-32(V)six modules and the SEWIP Block 1B3 High Gain Shipboard (HGHS) radar antenna radome integrated into the mast. This development represents the first international sale of the world's leading shipboard electronic warfare system, thereby significantly enhancing the vessel's defensive capabilities. Additionally, a hull-mounted sonar (HMS) will be integrated into the design.

Importantly, this will be the inaugural instance of a Japanese Aegis-equipped warship featuring radar panels mounted above the bridge, a configuration that mirrors that of the Spanish Álvaro de Bazán-class air warfare destroyers and their derivative, the Royal Australian Navy's Hobart-class. Furthermore, distinct from the AN/SPY-1 radar system utilised in Japan's existing eight Aegis destroyers (Kongō, Atago, and Maya classes), this new vessel will be equipped with the more advanced AN/SPY-7 AESA multi-function radar, which is also slated for installation on the Canadian River-class destroyers and the Spanish F-110 frigates.

The Aegis system-equipped vessels (ASEV) require a highly automated, low-maintenance, all-electric propulsion system due to their manning and electrical requirements. One effective option is the Combined Diesel and Gas (CODAG) propulsion system, which uses diesel engines for cruising and gas turbines that can be activated for high-speed transits. This system is currently utilised in the Japan Maritime Self-Defence Force's Hyūga-class and Izumo-class helicopter carriers, as well as the Mogami-class frigates. In May 2024, it was announced that the two ASEV warships would be equipped with Rolls-Royce MT30 gas turbines as their main propulsion system.

Current design

The initial design specifications for the two ASEV ships entail the construction of cruiser-sized warships, each with a standard displacement of 20,000 long tons (20,000 t). These vessels are projected to have an overall length of 690 feet (210 m) and a beam of 130 feet (40 m), utilising a monohull configuration. This overall size is intended to enhance habitability for the 110-member crew during extended deployments, facilitate simpler construction, and provide a stable platform for advanced sensors and weapon systems. Upon completion, these two warships are expected to be the largest surface combatants in operation within the Japan Maritime Self-Defence Force (JMSDF). According to Popular Mechanics, they are likely to be "arguably the largest deployable surface warships in the world."

Nonetheless, in November 2022, both Kyodo News and Jiji Press cited an unnamed senior official from Japan's Ministry of Defence, who suggested that the proposed ASEV warships might be scaled down to a size comparable to that of the Maya-class destroyers. This reconsideration follows concerns that the initially proposed beam would impair speed and manoeuvrability, thereby making the vessels more susceptible to detection and targeting by adversaries.

Procurement

In its published budget overview, the Japanese Ministry of Defence has allocated 22.8 billion yen (approximately USD 1.654 billion) for the initial procurement of advanced components related to the Aegis System Equipped Vessel (ASEV) program for Fiscal Year 2023. This investment is intended to "significantly improve ballistic missile defence capabilities, enabling the response to lofted and simultaneous ballistic missiles while also enhancing the capacity to address threats posed by hypersonic glide vehicles (HGVs) and similar challenges."

On April 4, 2023, the Japanese Ministry of Defence announced the execution of four contracts totalling 382.47 billion yen (around USD 2.83 billion) with Mitsubishi Heavy Industries (MHI) for the development of standoff defence weapon systems intended for the Japanese Self-Defence Force (JSDF).

Subsequently, on December 19, 2023, Defence Minister Minoru Kihara confirmed the approval of funding for the construction of ASEVs in Fiscal Year 2024 and Fiscal Year 2025, with commissioning scheduled for 2027 and 2028, respectively. The initial funding allocated for ASEVs in Fiscal Year 2024 is set at 373.1 billion yen (approximately USD 2.6 billion), representing a minor reduction from the 379.7 billion yen (around USD 2.64 billion) originally requested by the Japanese Ministry of Defence in its Fiscal Year 2024 budget proposal submitted in August 2023.

Armament

On November 17, 2023, the U.S. Department of State announced the authorization of a sale involving up to two hundred 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 Defence. 

A month prior, Japanese Defence Minister Minoru Kihara indicated intentions to procure Block IV Tomahawks, with a plan to accelerate the acquisition timeline by one year, as well as an outline for future purchases of Block V missiles. In a press conference held on November 20, 2023.

Subsequently, on March 28, 2024, the Japanese Ministry of Defence announced the commencement of Tomahawk missile training for personnel of the Japan Maritime Self-Defence Force (JMSDF), to be conducted under the auspices of the United States Navy. 

Criticisms

Senior Research Fellow Brent Sadler from The Heritage Foundation has articulated significant concerns regarding the proposed Advanced Small Echelon Vessel (ASEV) program. He argues that the provision of merely two units is grossly inadequate for maintaining a continuous operational presence of an Advanced Echelon Security Vessel (AESV) at sea. Sadler elaborated that a more conventional and efficient operational cycle would typically require a minimum of three vessels: one vessel actively deployed on a mission, a second vessel undergoing essential maintenance and refitting activities following its deployment, and a third vessel engaged in comprehensive training and work-up exercises to prepare for imminent deployment to relieve the first vessel.

In addition, Senior Defence Analyst Felix Chang from the Foreign Policy Research Institute (FPRI) underscored the susceptibility of the proposed ASEV warships to advanced Chinese anti-ship ballistic missiles, particularly the DF-21D and DF-26. The DF-21D, equipped with a range of approximately 1 500 kilometres, is specifically designed for anti-ship operations, while the DF-26, with an extensive range of up to 4,000 kilometres, poses a far-reaching threat to maritime assets and increases the operational challenges for ASEV vessels in contested waters.

Lastly, Senior Fellow Zack Cooper from the American Enterprise Institute highlighted the economic implications of adopting a sea-based ballistic missile defence (BMD) system compared to a land-based counterpart. He indicated that, from a financial perspective, a sea-based system does not present a more cost-effective alternative. In a 2020 report from Japanese media outlets, it was revealed that officials within the Japanese Ministry of Defence acknowledged the potential financial burden of alternatives to the land-based Aegis Ashore system, estimating that these alternatives could incur increases in costs of up to 50 per cent. This finding underscores the importance of carefully evaluating the economic viability and strategic effectiveness of defence systems in the context of national security.