January 1, 2021: In November 2020 South Korea launched its second KSS-3 submarine. The first one, the 3,300-ton Dosan Ahn Changho, began sea trials over a year ago and was supposed to enter service in 2020. While the sea trials were successful, some problems were encountered that require fixing before the Changho can enter service and that will probably take place in early 2021. It was announced that Changho broke the record for the time an AIP (air independent propulsion) equipped sub spent underwater. The duration of this feat was not released but since the current record is 18 days, the Changho had to stay under at least that long. It was implied that the South Korean sub remained submerged for over three weeks.

South Korea is building nine KSS-3 subs in batches of three. The second and third batches will each contain upgrades over the previous batch. All KSS 3 are high seas boats with endurance of 50 days, a 18,000 kilometers range and top speed of 37 kilometers an hour underwater and 22 kilometers on the surface. These boats are built to regularly operate throughout the Pacific. The KSS 3 boats are highly automated making it possible to get by with a crew of fifty. All are armed with eight 533mm torpedo tubes, four of them capable of launching Harpoon anti-ship missiles. KSS-3 Batch 1 has six VLS tubes for South Korean developed Hyunmoo-3C land-attack cruise missiles (1,500-kilometer range, 450 kg warhead) or Hyunmoo-3C ballistic missiles (800-kilometer range, half ton warhead). Batch 2 and 3 will have ten VLS tubes.

All nine KSS 3s are to be in service by 2029, at which point South Korea will have a fleet of 27 modern diesel-electric submarines. All KSS 3 boats have AIP and batch 2 and 3 will used the new lithium battery technology that Japan demonstrated in March 2020 when the latest of their Soryu class subs entered service. The Japanese navy put its first lithium-ion battery-equipped submarine into service. This sub is one of that two of the 12 boat Soryu class. This battery tech will be standard on the next class of Japanese subs.

If all these large diesel-electric subs sound like a smaller, non-nuclear, version of the American Virginia class SSNs (nuclear-powered attack sub), they are. The Australians pioneered this approach with their six Collins class boats that began entering service in 1996. The 3,100-ton Collins class subs had 70 days endurance and were meant to operate over vast distances in the Pacific Ocean. Japan followed with their 2,900-ton Soryus in 2007.

The large South Korean and Japanese submarines forces exist to deal with the immediate threat from North Korea and the potential threat from Russia and China.

North Korea has 70 subs, but only twenty are large subs and these are all elderly Romeo class boats. The Russian Romeo class was the successor to the Whiskey class boats, which were, in turn, based on the German Type XXI which first showed up in 1943. This was the first modern submarine in that it was designed to spend most of its time underwater. with just the snorkel device and periscope above water, to bring in air for the diesel engine and crew. The Type XXI was a 1,600-ton (on the surface) sub, compared to the 1,500-ton Romeos. Russia built over 500 Romeos, while China built over 80. The rest of the North Korean subs are much smaller, of more recent construction and are used mainly for delivering commandos or spies or ambushing larger ships along the coast. Only a few of the North Korean Romeos are operational and these are the only subs that can operate away from the coastal waters. North Korea is building at least one diesel-electric sub that can launch a locally developed ballistic missile.

China currently has about fifty modern diesel-electric subs in service. All are based on the Russia Kilo and the latest ones improve quite a bit on the Kilo. China also has twelve nuclear attack subs, which are not as effective as Russian or American designs. Russia has seven nuclear attack subs in its Pacific Fleet, along with two Kilos. All the Russian and Chinese nuclear subs available in the Pacific are outnumbered by the American nuclear attack subs assigned to the Western Pacific.

South Korea has nine 1,200-ton KSS-1 boats and nine 1,800-ton KSS-2s. All are German designs with most built in South Korea. The KSS-2 is based on the German Type 214 and has AIP (Air Independent Propulsion) that enables it to remain under water for more than a week at a time. The KSS-1s were built, mostly in South Korea, during the 1990s and are based on the Type 209.

In June 2019 South Korea completed refurbishment of its nine German Type 209 subs. The refurb takes about two years and involves installing new electronics as well as a towed array sonar. The refurb makes these boats capable of serving into the 2030s.

The growing South Korean submarine force had by 2015 become a major part of the fleet. In recognition of this, in early 2015 South Korea created a new Submarine Command whose main purpose is to develop better anti-submarine capabilities against North Korea or even China. Another reason for the Submarine Command was to make it easier to curb the procurement corruption that has developed in the navy. Several senior navy officers and officials had been prosecuted for this sort of misbehavior. Since the submarine service is rather elite and much more sensitive to getting the most for their money, the Submarine Command, run by submarine officers, is expected to be more resistant to corruption. That is important because South Korea is putting a lot more money into submarines.