Japan will build two more Aegis-equipped destroyers to replace two land-based ABM (Anti-Ballistic Missile) systems cancelled earlier in 2020. Japan cancelled the two Aegis Ashore ABM systems, looked at the alternatives and decided the best one was two more Aegis ABM warships. This is not as effective as Aegis Ashore which, as a land base, was cheaper to maintain and always available to defend against North Korean or Chinese ballistic missiles. Ships have crews and ships spend only about a third of their time at sea and because of the Aegis Ashore problem, Japanese warships would not be able to use their Aegis ABM system while in port.
The Aegis Ashore cancellation was the result of poor planning back in 2017 when it was decided to install the Aegis Ashore systems in two existing military bases. This decision was encouraged by the fact that in 2016 the first Aegis Ashore system became operational in Romania. The second one became active by 2018 in Poland. Unfortunately, Japan is not like Romania and Poland, two nations that suffered decades of brutal Russian occupation and are desperate for protection from revived Russian aggression.
Japan has prospered greatly under the protection of the American military after World War II and developed some bad habits when it came to defense matters. What killed the Aegis project were several of those bad habits. First, as defense officials were working out the details they soon found they had underestimated the cost of preparing the two Aegis Ashore sites. That cost was about 25 percent higher than estimated. Costs threatened to increase still more when civilians living near the two Aegis base areas discovered that there were side-effects from the use of Aegis missiles. Planners made some adjustments to the area Aegis would occupy but that was not enough to assure local civilians that the booster portion of the two-stage SM-3 missile would never fall in or near a populated area. In one Aegis Ashore site there were civilian concerns about living too close to the AESA radar Aegis uses to detect and track incoming missiles. Once the Japanese media and local politicians get hold of issues like this, they stay active until the “threat” goes away. North Korean and Chinese missiles are seen as less of a threat. In Poland and Romania, Russia is always seen as the primary threat and the side effects of using Aegis are not an issue.
North Korea remains the primary threat to Japan with China a distant second. North Korea's unwillingness to get rid of its ballistic missile and nuclear weapons programs persists. As a result, Japan is still moving ahead to expand its ballistic missile defenses. Most of these will still be based on the Aegis system, which is normally installed on large (8,000 tons and up) warships. Japan has eight of these Aegis anti-missile system destroyers in service or under construction and due to enter service in 2021. The two additional Aegis destroyers won’t enter service until 2026. That will give Japan ten of these ABM equipped ships, second only to the United States with 33. The U.S. also has 51 other warships with Aegis systems that only handle anti-aircraft defense. Some of these ships could be upgraded but most of the non-ABM ships are elderly and approaching retirement.
The two land-based Aegis Ashore anti-missile systems were not expected to be in service until 2024. At that point, Japan would have eight Aegis anti-missile systems and could have two more Aegis anti-missile destroyers by 2024 by upgrading the Aegis systems on two of the older destroyers. That upgrade was considered after Aegis Ashore was canceled but building two more Aegis equipped destroyers was determined to be a better investment.
It appears that North Korea will continue to be a threat while how much more of a ballistic missile threat China becomes is still considered less of a problem. China has a long history of threatening but not acting. North Korea has demonstrated an ability to attack without warning and did so in 2010. North Korea has always been less cooperative than China although the Chinese are still a threat.
The newest Japanese destroyers are the two 10,200-ton Maya class ships and two new ships to be built will probably be two more Mayas. These are improved versions of the earlier Atago class destroyers. The Mayas also borrow much from the first four Japanese Aegis-ABM ships, the 9,500-ton Kongos, which were built during the 1990s and modeled on the American Burke class Aegis destroyers. The Kongos have 90 VLS (Vertical Launch System) cells for anti-aircraft/missile missiles as well as ASROC anti-submarine rockets. These carry an anti-submarine torpedo to, in effect, extend the range of the torpedo by 22 kilometers. Japanese Burke type destroyers also carry a 127mm (five-inch) gun and eight Japanese designed anti-ship missiles (similar to the American Harpoon). The Maya class has 96 VLS cells (as do Atagos) as well as more advanced electronics that enable the Mayas to link with the U.S. Navy CEC (Cooperative Engagement Capability) that allows real-time sharing of sensor and other data in real-time between other CEC equipped ships and even shore-based systems like Aegis Ashore.
What prompted the original Aegis Ashore order was the 2017 decision that Japan did not need the more expensive THAAD anti-missile system when it realized that two land-based Aegis systems on the main island could do the same job at less cost. That plus the Aegis equipped destroyers armed with the SM-3A anti-missile missile would enable those two land-based Aegis systems to protect all three of the home islands.
In addition, Japan has 24 Patriot anti-aircraft missile batteries that can also fire the PAC-3 anti-missile missile. The PAC-3 has one drawback; it only has an effective range of 30 kilometers against incoming missiles. The Aegis SM-3 anti-missile missile has a range of from 700 kilometers (older Block 1) to more than three times that for the later Block II models. This is why two Aegis land-based systems can protect most of Japan (the main island). The Patriot PAC-3 provides local defense for key targets (the capital and major military bases).
Japan also took the lead in developing an upgraded version of the SM-3 missile that can intercept ICBMs. This version recently had its first test against an incoming ICBM warhead and was successful. Japan does not need the ICBM upgrade to defend against North Korean missiles but would if the warheads were from China.