Pete Comments
In its Central Asian region Russia maintains powerful forces of nuclear armed long range bombers and ICBMs. Russia's Pacific Fleet also contains many SSKs, SSNs and SSBNs all a potential threat to Japan. China is rapidly increasing its conventional and nuclear naval forces to rival Russia's with China also presenting many potential threats to Japan. North Korea is also a threat with steadily improving and potentially nuclear armed long range missiles - sometimes being test flown over Japan's home islands and territorial waters.
In the face of this Japan is increasing its defense budget to amounts and percentages of GDP not seen since World War Two. See Naval News' August 31, 2023 article "Japan Requests Largest Defense Budget Ever".
Japan’s Fiscal Year FY2024 Defense budgetary request of 7.7 Trillion Yen (US$52.9 Billion), an increase over FY2023’s budget of US$46.8 billion.
But when one compares US$52.9 Billion with Japan's US$4,410 Billion 2023 nominal GDP Japan's defense budget is still only 1.2 percent of Japan's
GDP. Yet Japan's defense budget is growing rapidly. Japan's defense industry is
also highly efficient.
Aegis system equipped vessel (ASEV). (Courtesy Japan MoD image via NavalNews).
Amongst items requested are
Modifications of Japan’s JS Izumo and JS Kaga defacto aircraft carriers (US$290 million) to better accommodate F-35Bs. Modification of Kawasaki P-1 maritime patrol
aircraft (MPA) to emphasize electronic
warfare (US$95.7 million).
wispywood2344
To meet these threats Japan is gradually improving its high tech defenses. To that end long term contributor wispywood2344 on September 9, 2023, reports on three weapon systems:
Among the 17 R&D projects included in Japan’s Fiscal Year FY2024 Defense
budgetary request, I would like to introduce matters related to "Submarine
Matters".[1] 
A) Combat Support Multipurpose Unmanned Surface Vehicle (USV) [2].
The outline is as follows:
1. Selective equipment; sensor (possibly sonar and ESM antenna),
anti-ship-missiles, anti-submarine-torpedoes, etc. .
2. Submersible for stealth.
3. Remotely controlled via SATCOM.
4. Automatic navigation in bad sea state.
5. Able to act as a fleet" in cooperation with multiple USVs.
6. This project will cost 24.5B yen (US$167,587,355 in total and complete by FY2030.
[NavalNews reports: To quickly acquire knowledge of USV operation and promote the development of domestically produced USVs, the Japanese defense budget calls for the procurement of USVs that have been used in various countries as test equipment.]
B) Improvement of Type12 Lightweight Torpedo (LWT) (photo above) [3].
The outline is as follows;
1. Add anti-torpedo (hard-kill) capability to Type 12 Lightweight Torpedo (LWT).
2. Improve the surface ship sonar, to enable effective operation of
improved Type 12 LWT.
3. This project will cost 12.5B yen (US$85,525,746) in total and complete by FY2029.
Artwork courtesy Raytheon of a GPI concept (via NavalNews).
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C) Japan-U.S. joint development of
"Glide-Phase-Interceptor" (GPI) [4].
The Japanese MoD starts development of land-based Glide Phase Interceptor system (artwork above) used against Hypersonic glide vehicles (HGVs) this year. [5][6][7]
[Project may cost equivalent to US$512.7 million]. From next year onward, it will participate in the US's ongoing development project of sea-based GPI system. Also see hereand here.]
In my opinion, Japan will be responsible for the upper stage rocket motor, similar to the Japan-US jointly developed SM-3 Block IIA. [see references to Japan here.]
[1] https://www.mod.go.jp/j/policy/hyouka/seisaku/2023/jizen.html
[2] https://www.mod.go.jp/j/policy/hyouka/seisaku/2023/pdf/jizen_01_honbun.pdf
[3] https://www.mod.go.jp/j/policy/hyouka/seisaku/2023/pdf/jizen_16_honbun.pdf
[4] https://www.mod.go.jp/j/policy/hyouka/seisaku/2023/pdf/jizen_17_honbun.pdf
[5] https://www.mod.go.jp/j/approach/hyouka/seisaku/2022/pdf/jizen_12_logic.pdf
[6] https://www.mod.go.jp/j/approach/hyouka/seisaku/2022/pdf/jizen_01_logic.pdf
[7] [See cool animated video of a GPI in action] https://www.youtube.com/watch?v=PzUFHvvUNGU#t=3h09m31s