Recently, Kawasaki Heavy Industries carried out the first phase of the Japan Maritime Self-Defense Force's helicopter destroyer Izumo, giving it carrier-like functions. The retrofit included the addition of vertical take-off and landing decks, the use of high-temperature materials, the demarcation of takeoff and landing markings, and the expansion of hangars. Subsequently, an F-35B fighter, part of the US Marine Corps, successfully carried out its first vertical takeoff and landing.
As the Izumo undergoes its second phase of carrierization, it will truly become an aircraft carrier that can carry up to 18 F-35B fighters. The Kaga, a ship of the same class, will quickly carry out similar modification work after the completion of the "Izumo" modification. This would give the Japan Maritime Self-Defense Force two light carriers, making it the third naval nation in the world to be equipped with fifth-generation aircraft.
However, this series of modification measures violated the provisions of the Japan-US postwar agreement that Japan could not own aircraft carriers. Nevertheless, Japan has been trying to break through this limitation, not only by carrierizing helicopter destroyers, but also by importing medium-range missiles from the United States for off-island attacks if needed.
Recently, media reports said that the Japan Maritime Self-Defense Force also plans to venture into the field of nuclear submarines, trying to obtain equipment and licenses for nuclear submarines. The plan, which stemmed from the transfer of nuclear submarines by the United States to Australia, set off a chain reaction. A number of Japanese prime ministerial candidates have publicly stated that the Japanese government should seriously consider the need to equip nuclear submarines.
In fact, Japan began to equip "quasi-nuclear submarines" as early as October last year, the first of which was called "Big Whale". The "Big Whale" class submarine is a conventionally powered submarine with a displacement of 3,000 tons. It uses lithium-ion battery technology and diesel hybrids and is capable of firing Type 89 torpedoes and Harpoon anti-ship missiles. Compared with the previous Soryu-class submarines, the Big Whale class has significantly improved its displacement, becoming the world's second largest conventionally powered submarine, second only to South Korea's "Dosan An Changho".
This change represents a revolution in the way Japanese submarine construction is done. Lithium-ion battery submarines are better at quietness, replacing traditional propellers with pump-displacement jet thrusters to drastically reduce noise. This puts its performance close to that of the French Ruby small nuclear submarine, but with one less nuclear reactor than the nuclear submarine.
Given that the Japan Maritime Self-Defense Force mainly performs defense missions in the surrounding waters and has no need for ocean-going operations, the Big Whale-class submarine can be regarded as a kind of nuclear submarine, posing a serious threat to the maritime security of neighboring countries.