The warship was unveiled at a ceremony at the Yokusuka naval base near Yokohama, also home to the U.S Navy's Seventh Fleet.
The Izumo has a crew of 470, and with a standard displacement of 19,500 tones (24,000 tonnes at full load, according to military publication Jane's
), it is as large as the storied Yamato-class battleships which fought U.S. naval forces in the Pacific theater of World War II.
The wreck of one of the two Yamato-class battleships, the Musashi, was discovered
early in March 2015 by Microsoft co-founder Paul Allen.
At 241 meters (791 feet) in length, the Izumo is 51 meters (167 ft) longer than the Hyuga, another helicopter carrier which was, until now, the MDSF's largest vessel.
Violating the constitution?
Regional neighbors and rivals questioned the legitimacy of such a ship for purely defensive purposes, pointing out that, due to its size and deck configuration it could be repurposed as an aircraft carrier -- a class banned under Japan's pacifist constitution.
"The Izumo proves that Japan has the technical capabilities and demand to develop aircraft carriers. It's also possible that Japan may explore the possibility during the Izumo's service," Li Jie, a Beijing-based military expert, told the Chinese state-backed Global Times
However, Defense Minister Gen Nakatani told reporters in Yokohama that the MSDF did not intend to use it in this way.
"We are not thinking about using this as an aircraft carrier," he said, saying that the lack of hangers and service bays, along with a deck unsuitable for takeoffs and landings, meant that the Izumo wasn't designed for fixed-wing aircraft.
He said that it needed to be as large as it is so it could host joint operations and act as a command center. He insisted that the new addition to Japan's maritime forces was designed for peaceful purposes.
"The vessel can serve in a wide range of roles including peacekeeping operations, international disaster relief and aid."
He added that its helicopter capabilities -- it can host seven anti-submarine patrol helicopters, plus two rescue and transport helicopters, the Japan Times
reported -- would aid in the detection of sophisticated Chinese submarines.
Japan, along with the Philippines and Vietnam, is engaged in territorial disputes with China over the sovereignty of islands in the South China Sea, and Kazuhisa Ogawa, a defense analyst at the Strategic Research Institute of International Change in Japan, says that, in combination with Japan's other helicopter carriers, the Izumo could be used to "regain remote islets."
He also downplayed China's suggestions that the size of the Izumo represented an escalation of Japan's military ambitions, telling CNN that although it is the biggest Japanese military ship since World War II, it is only a fifth of the size of the USS George Washington.
"It would cost five times Japan's current defense spending for the SDF to have an independent operational capability. The Japanese public would not take that kind of risk," he said.
The commissioning of the Izumo comes amid heightened tensions between Japan and its neighbors China and South Korea. In July. Japanese Prime Minister Shinzo Abe allowed for a reinterpreting
of Japan's constitution, paving the way for more active military engagement overseas.
The Chinese government has also invited the Japanese leader to attend a ceremony in the Chinese capital in September to mark the 70th anniversary of the end of the Second World War.
Japan's handling of its wartime aggression is frequently criticized by China and other Asian nations -- it is often accused of downplaying its actions during the war.
Chinese foreign ministry spokeswoman Hua Chunying said Tuesday that the Chinese government had contacted "all relevant countries" with a view to attending.
The Japanese Yomiuri Shimbun
newspaper said that, as the celebrations will feature a military parade, Abe is "unlikely to attend."
It quoted an unnamed Foreign Ministry official as saying: "While the Japanese government is demanding China improve the transparency of its defense spending, attendance of the prime minister is impossible."
Japanese Chief Cabinet Secretary Yoshihide Suga has previously said that China should work on developing a future-looking cooperative relationship with Japan, rather than highlighting Japan's previous, 70-year-old indiscretions.