Japans

Japan’s Ministry of Defense has included an intriguing description of the ASM-3 Kai missile in its record fiscal year 2027 defense budget request, referring to the weapon as an “air-to-surface/anti-air missile.” Until now, the ASM-3 family has been publicly associated with the air-launched anti-ship (anti-surface) mission, and the wording potentially hints at an additional capability or intended role for the upgraded weapon.

The reference appears in Japan’s FY2027 defense budget request, submitted today, which seeks a record ¥8.89 trillion (approximately $56 billion) for the fiscal year beginning in April 2027. The request is part of a broader push by Tokyo to expand standoff strike, air defense, uncrewed systems, and other advanced capabilities.

The reference appears under a sub-section entitled Durability and Resilience, which calls for funds to “secure ammunition and fuel, increase the number of operational units (by addressing parts shortages, etc.), enhance the resilience of facilities (through facility upgrades associated with the formation of new units and the introduction of new equipment, etc.), and strengthen the operational infrastructure (by enhancing manufacturing capabilities, etc.).”

In terms of securing ammunition, the document highlights the breadth of weapons systems involved, ranging from 5.56mm small arms ammunition and 30mm cannon rounds, via 155mm precision artillery rounds, up to advanced missiles including the Type 23 ship-launched air defense missile and the ASM-3 Kai.

The Mitsubishi Heavy Industries (MHI) ASM-3 is Japan’s domestically developed supersonic air-launched anti-ship missile, originally intended to arm the Mitsubishi F-2 fighter. The improved ASM-3 Kai (“Kai” meaning modified or revised) represents a significant evolution of the weapon, although the full nature of its capabilities and performance have not been officially revealed. The missile has already been observed undergoing testing on F-2s.

The ASM-3 program has also gone through a number of different configurations over its development history, with at least five distinct external configurations identified in previous reporting. The existence of multiple iterations leaves open the possibility that the newly identified “anti-air” designation could ultimately correspond to a dedicated air-to-air variant or derivative of the ASM-3 family, rather than simply a secondary capability of the baseline ASM-3 Kai.

Reportedly, the ASM-3 Kai is capable of flying more than 400 kilometers (about 250 miles), although the exact range of the operational weapon remains classified. It is powered by a ramjet engine, giving it sustained high-speed performance — reportedly around Mach 3. If it indeed has an air-to-air capability, this would be an advantage in some scenarios, compared to relying solely on a brief but very powerful rocket boost as many air-to-air missiles do.

The weapon is also understood to employ an active/passive radar seeker, providing it with both an active radar mode for detecting and engaging targets and a passive mode that can home in on their electromagnetic emissions. While an active radar seeker is common on long-range air-to-air missiles, the latter passive capability could also be of extreme value in an air-to-air application.

The ASM-3 is also a substantially larger missile than typical fighter-launched air-to-air weapons. While that imposes obvious carriage and aerodynamic penalties, it also allows for a larger propulsion system, seeker, and warhead than would be practical in a smaller missile.

A weapon capable of traveling hundreds of miles at high speed, while carrying an active/passive radar seeker, could potentially be especially useful against high-value airborne assets such as airborne early warning and control (AEW&C) aircraft. These platforms provide vital wide-area surveillance, battle management, and targeting capabilities. At the same time, their powerful radars are necessarily emitting, potentially making them detectable and trackable by a missile employing a passive seeker.

China’s rapidly expanding AEW&C fleet is an increasingly important part of its ability to generate situational awareness, coordinate fighters, and extend its sensor coverage well beyond its immediate borders. The force, which already numbers dozens of increasingly capable fixed-wing aircraft, is a growing operational challenge for Japan and other regional air forces.

The ability to threaten such aircraft from well beyond the range of conventional air-to-air engagements could force an opponent to operate its AEW&C fleet even further from contested airspace, reducing the effectiveness of its sensors and command-and-control architecture. Although a passive seeker could also offer an avenue for homing in on relevant radar emissions, exactly how the ASM-3 Kai’s seeker would operate against airborne targets is not publicly known. Equally, a different variant of the missile, optimized for anti-air missions, could incorporate both passive and active seekers specially adapted for that mission set, although it is very possible a single configuration can accomplish both missions. As well as AEW&C aircraft, such a missile would be just as relevant for other high-value, non-maneuvering targets at long ranges, including intelligence-gathering platforms, tankers, and other support aircraft.

The budget language by itself falls short of establishing whether the ASM-3 Kai has been tested or validated against aircraft. The designation could reflect a broader classification within the budget documents, or it could point toward a genuine expansion of the weapon’s intended target set.

XASM-3 Supersonic anti-ship missile test launch

Such a weapon would not necessarily be a replacement for Japan’s existing air-to-air missile arsenal. Instead, an “anti-air” ASM-3 Kai could occupy a specialized niche focused on high-value or otherwise particularly important airborne targets at extended ranges.

The possibility is consistent with Japan’s broader effort to expand the flexibility and reach of its air-launched weapons. Tokyo is pursuing a growing family of standoff weapons as part of a major expansion of its counterstrike and deterrence capabilities, including longer-range missiles capable of striking targets well beyond the immediate vicinity of Japan.

Other air-to-air missiles mentioned in the same section of the document comprise the U.S.-made AIM-120 Advanced Medium-Range Air-to-Air Missile (AMRAAM) and the domestically developed AAM-4B, another medium-range weapon, thought to be the first of its kind to be fitted with an active electronically scanned array (AESA) antenna.

Between the exclusive AESA radar and Japan’s labour cost, Mitsubishi’s AAM-4B might be the most expensive air-to-air missile on the planet pic.twitter.com/rfBnXB8RzS

— Lia Wong (@LiaWong__) May 3, 2022

The FY2027 defense budget request also mentions another apparently new air-launched weapon for Japan, the AGM-88G Advanced Anti-Radiation Guided Missile-Extended Range (AARGM-ER). Japan has not previously been publicly documented as an international AARGM-ER customer, but the weapon would be an obvious candidate for integration with its F-35 fighters if it wishes to bolster their suppression/destruction of enemy air defenses (SEAD/DEAD) capabilities.

In terms of F-2-related developments, the document calls for the upgrade of an initial 10 of these aircraft to make them compatible with the air-launched version of the Upgraded Type 12 anti-ship guided missile, a significant new weapon that you can read more about here.

TWZ has contacted Japan’s Ministry of Defense seeking clarification on the “air-to-surface/anti-air” designation and what it means for the ASM-3 Kai’s intended capabilities and target set. It could also be the case that the description is an error in the budget document.

However, the emergence of such a capability would also come at a time when very-long-range air-to-air weapons are becoming increasingly important as anti-access/area-denial challenges make it harder for fighters to get close to enemy aircraft and the high-value assets supporting them. China has fielded weapons such as the PL-15 and the much larger PL-17, while the United States is developing the AIM-260 and has just revealed the AIM-424 Malice, a U.S. Navy missile reportedly capable of reaching more than 250 nautical miles. The U.S. Navy is also fielding the AIM-174B, a very-long-range weapon developed very much with the Chinese threat in mind, and which we discuss in the video below.

How The Navy’s New Very Long-Range AIM-174 Will Pierce China’s Anti-Access Bubble

For now, exactly what prompted the “air-to-surface/anti-air” designation for the missile is unclear, but if it reflects a genuine expansion of the ASM-3 Kai’s mission set, it would represent a particularly interesting development in Japan’s rapidly evolving air-launched weapons portfolio.

Hat-tip to Yoshihiro Inaba for bringing this development to our attention.

Contact the author: thomas@thewarzone.com

The first of Japan’s two new cruiser-sized Aegis System Equipped Vessels (ASEV) is continuing to take shape, recently receiving its huge main integrated mast, giving the vessel a new and remarkably imposing silhouette. The four very large fixed arrays for the ship’s powerful AN/SPY-7(V)1 radar will eventually be integrated onto this structure. The ASEV’s stated primary mission is missile defense, but Japanese authorities plan to give the vessels additional counter-drone, anti-ship, and land attack capabilities in the future. Tomahawk cruise missiles are notably set to be added to the ship’s arsenal down the line.

The ASEVs are large surface combatants, set to be some 620 feet long, have a beam (the widest point of the hull) of some 82 feet, and a standard displacement of 12,000 tons. For comparison, Japan’s largest surface combatants today, its Maya class destroyers, are just over 557 feet long, have a beam of some 73 feet, and a standard displacement of around 8,200 tons. It is worth noting here that the size of new and advanced destroyers, often optimized for anti-air warfare missions, has been trending upward globally in recent years. This, in turn, has caused the line between destroyers and what have more historically been categorized as cruisers in certain cases.

The first ASEV was laid down at Mitsubishi Heavy Industries’ (MHI) shipyard in Nagasaki in July 2025. The second was laid down in February of this year at Japan Marine United Isogo shipyard, which is situated in Yokohama City near Tokyo, according to a past report from Naval News. The Japanese Ministry of Defense is currently aiming to have the first of these vessels in service before the end of the country’s 2027 Fiscal Year, which runs from April 2027 to March 2028. The second is expected to follow in the 2028 fiscal cycle, which extends into 2029.

Significant progress in the overall construction of the first ship has been made just this year. The addition of the main mast structure, installed on top of the main superstructure, as seen in pictures at the top of this story and below, has drawn particular attention in recent weeks.

The especially large size of the ASEV’s integrated mast is driven by that of the AN/SPY-7(V)1 active electronically-scanned array (AESA) radar from Lockheed Martin. Each one of the radar’s four rectangular arrays is reportedly around 14 feet (nearly 4.3 meters) tall. This would put them in the same general size category as the arrays for Raytheon’s AN/SPY-6(V)1 Air and Missile Defense Radar (AMDR) found on U.S. Navy Flight III Arleigh Burke class destroyers. That being said, the pictures we have now raise the question of whether the AN/SPY-7(V)1 arrays are bigger than previously assessed. The AMDR is another notably large design heavily optimized for missile defense.

The size and location of the mast provide a centralized, elevated position for the AN/SPY-7(V)1’s large arrays, which will also require significant power generation capacity and thermal management to keep everything cool. This is a notable departure from the placement of the arrays on the main superstructure on existing Japanese destroyers, as well as the U.S. Arleigh Burke class, and offers an unobstructed, elevated line-of-sight to the horizon. Beyond the ballistic missile defense mission, this view farther out over the horizon would be important for tracking and engaging low-flying drones and cruise missiles, which might be targeting the ship itself. This is something we will come back to later on.

“With five times the tracking capability of the SPY-1, it [the AN/SPY-7(V)1] counters lofted trajectories and simultaneous multiple ballistic missile threats,” according to a machine translation of a section of the Japanese Ministry of Defense’s 2026 defense policy white paper, which was released earlier this month.

The passive electronically-scanned array (PESA) AN/SPY-1 was the first radar to be paired with the Aegis Combat System, and both were first introduced in the 1970s. Variants of the SPY-1 are still found on a variety of U.S. and foreign Aegis-equipped warships, including Japan’s Kongo, Atago, and Maya class destroyers.

The AN/SPY-7(V)1 is also a derivative of the U.S. military’s static, land-based Long Range Discrimination Radar (LRDR) in Alaska. Japan also originally planned to employ the AN/SPY-7(V)1 on land at a pair of Aegis Ashore missile defense sites. However, that effort was subsequently cancelled, with the ASEV emerging to fill the resulting gap.

Additional versions of the AN/SPY-7 with much smaller arrays are also being integrated onto new F110 Bonifaz class frigates for the Spanish Navy and the Royal Canadian Navy’s forthcoming River class destroyers (also known as the Canadian Surface Combatant). The use of the AN/SPY-7(V)1 on the ASEV could impact decisions regarding new radars for other future and existing Japanese warships. Raytheon is also pitching versions of its increasingly popular AN/SPY-6 family for use on a successor to the Kongo class and for refit on the Maya class, according to a recent report from Naval News.

When it comes to the ASEV, as already noted, the AN/SPY-7(V)1 is central to the ship’s main stated missile defense mission. As the name makes clear, the ship will also feature the Aegis Combat System. The vessel will be capable of “remote engagement and guidance against anti-air targets tracked by other vessels” via a “Cooperative Engagement Capability (CEC),” per the Japanese Ministry of Defense’s most recent annual defense white paper.

The video below provides details about the U.S. Navy’s Cooperative Engagement Capability (CEC) developments, which are likely very similar to what Japan has planned for the ASEV.

Cooperative Engagement Capability

In terms of armament, when the ASEVs first enter service, their main weaponry is expected to be a mix of variants of the Standard Missile-3 and -6 (SM-3 and SM-6). The SM-3 family is designed to engage ballistic missile threats during the mid-course portion of their flights while they are traveling outside of the Earth’s atmosphere. The SM-3 also has a demonstrated anti-satellite capability. The SM-6 is a multi-purpose missile that was originally designed with an anti-air focus. It can be used to target incoming ballistic missiles in the terminal phase of flight and also has at least a degree of capability for engaging hypersonic weapons. SM-6 can be used in a surface-to-surface mode, including against ships, as well. Japan is also a partner in the U.S.-led development of a new Glide Phase Interceptor (GPI), which is being designed specifically to intercept unpowered, but highly maneuverable hypersonic boost-glide vehicles.

SM-3, SM-6, and future GPIs will be loaded into either of the ASEV’s two Vertical Launch System (VLS) arrays, one at the bow end and another toward the stern. Each one of the ships will have a total of 128 VLS cells. For comparison, Japan’s Maya class destroyers, as well as the U.S. Navy’s Flight IIA and III Arleigh Burke class destroyers, have 96 VLS cells apiece. The U.S. Navy’s Ticonderoga class cruisers each have 122 VLS cells, and 128 is also the number of VLSs currently expected to be found on the future Trump class battleships.

At the time of writing, Japanese authorities do not appear to have explicitly mentioned plans to arm the ASEVs with other missiles when they first enter service. That being said, any VLS array capable of accommodating SM-3s and SM-6s should be able to fire a variety of other weapons, including shorter-ranged SM-2s and Evolved Sea Sparrow Missiles (ESSM), which the ship could use for more localized air and missile defense, as well as protecting the ship itself.

Renderings and models of the ASEV do show the design also armed with a five-inch naval gun in a turret on the bow, along with two Phalanx Close-in Weapon Systems (CIWS) and other automatic cannons for point defense.

As mentioned, while missile defense is the immediate focus for the ASEVs, there are already plans to significantly expand their capability to engage other ships and targets on land. Tomahawk cruise missiles and a new, extended-range version of the Type 12 anti-ship cruise missile are set to be added to the arsenal of these vessels in the 2032 timeframe, according to the latest official Japanese defense white paper.

Japanese authorities want the ASEVs to eventually be able to help fend off waves of enemy drones, too. High-energy laser-directed energy weapons are set to be integrated onto the ships down the line to help address those threats. The overall size and other general characteristics of the ships would leave the door open to the possible addition of high-power microwaves and other capabilities in the future.

TWZ has long noted that the ASEVs will bring huge new boosts in naval air and missile defense and long-strike capability to the Japan Maritime Self-Defense Forces. The vessels also reflect a significant evolution in post-World War II Japanese doctrine, toward what officials currently frame as a “stand-off defense” construct that remains within the bounds of the country’s current pacifist constitution.

Just with SM-3, SM-6, and GPI, the ASEVs will offer an important addition to the air and missile defense bubbles around Japan’s home islands and outlying territories in the face of growing geopolitical friction with China and Russia, two countries that are increasingly cooperating militarily. The vessels will also add to Japan’s deterrent against long-standing and still evolving threats posed by the regime in North Korea, which has its own close ties to the Chinese and Russian governments. All three of these nations continue to expand their arsenals of ever-more capable ballistic, cruise, and hypersonic missiles. Long-range one-way-attack drones are another growing part of the equation, with the ongoing conflict in Ukraine and fighting in the Middle East in recent years underscoring just how real a threat they pose.

With the addition of Tomahawks, the ASEVs, along with other Japanese warships, will gain the additional ability to threaten counterstrikes against targets on land (and potentially at sea) at least around 1,000 miles in any direction. As part of the broader stand-off defense strategy, the Japan Self Defense Forces is developing new land-based long-range strike capabilities, including hypersonic missiles, as well.

It is worth noting that with current plans to acquire only two ASEVs, these will be high-value but also low-density assets, which will have to be very deliberately deployed for maximum effect. They will also stand out as top-priority targets in any future conflict, and will need to be protected as such.

It is possible that the roles and missions of the ASEVs, just like their designs, could evolve further as time goes on. The threat ecosystem facing Japan will continue to evolve, likely more rapidly, in the coming years. The country is also expanding its naval capabilities in other ways, and with an eye toward more blue water operations. This includes expanded light carrier capabilities through refits of existing Izumo class ships. Anti-ship ballistic missiles and hypersonic cruise missiles, among large volumes of more traditional threats, could see the ASEVs used as escorts, even if experimentally. While just two hulls are barely enough to keep one on patrol to protect Japan, more could be built for expeditionary applications.

Regardless, the ASEVs are set to be a major addition to the Japan Maritime Self Defense Force’s fleets that will have big ramifications. From the progress that is visible at the shipyard in Nagasaki, MHI looks to be well on track to deliver the first of these ships next year or two.

Special thanks to @kensakai9310 on X, who also goes by “Sakai,” for sharing recently taken pictures of the first ASEV under construction at MHI’s yard in Nagasaki with us.

Contact the author: joe@twz.com