MELBOURNE, Australia — Japan has launched the first of a new class of diesel-electric submarines, which will complete the U.S. ally’s planned expansion of its submarine fleet to 22 boats when it enters service.

The new submarine, which has been named the Taigei, meaning Big Whale, was launched at the Mitsubishi Heavy Industries shipyard in the city of Kobe on Wednesday. It is the first of a successor class to Japan’s current Soryu-class boats.

The Taigei is a 3,000-ton diesel-electric attack submarine measuring 84 meters (275 feet, 7 inches) long. The design was previously known as the 29SS class, named after the 29th year of Emperor Akihito’s reign in Japan, which corresponds to the year 2017 in the Gregorian calendar.

Like the last two boats of the Soryu class, the Taigei will be equipped with lithium-ion batteries as a power source. Japan has conducted extensive research into the use of lithium-ion batteries onboard submarines since the early 2000s, and says they require less maintenance and are capable of longer endurance at high speeds while submerged, compared to lead-acid batteries.

Japan is the only known country to have operational submarines using lithium-ion batteries.

The Taigei will now undergo fitting out and sea trials at the builder before it is commissioned into the Japan Maritime Self-Defense Force in 2022. When operational, it will become the 22nd submarine in service with the force, completing plans to increase Japan’s sub fleet to 22.

The upsized submarine force will be composed of nine older Oyashio-class submarines, 12 Soryus and the Taigei. Japan has plans for two more Taigei-class submarines, and has asked for $654.1 million for one more boat in the Defense Ministry’s latest budget request.

The decision to increase the submarine force from 16 boats was announced in the 2010 National Defense Program Guidelines, and comes as Japan continues to cast a wary eye on China’s military modernization and increasing assertiveness in the region.