Japan's major straits (with possible patrol details below)
[According to this open source] During the Cold War the Japanese Navy's active 16 submarines mainly watched three straits for Russian subs. At any one time around 3 submarine may have been available to watch each of the following straits:
- the Soya Strait [aka La Perouse Strait) (between Hokkaido and Russia's Sakhalin island),
- the Tsugaru Strait (between Honshu and Hokkaido), and
- the Tsushima Strait between Kyushu and South Korea.
Since the end of the Cold War and with the rise of Chinese naval power, some of Japan's subs have been diverted to patrol waters in the East China Sea around the Nansei (aka Ryukyu) Islands (island chain between Kyushu and Taiwan). Japan now has 18 active (Oyashio and Soryu class) submarines, with plans to raise the number to 22 by 2018.
US Air and Naval Bases in Japan, (not too many Japanese Base maps available!) But note:
- the Japanese Navy's s fleet and sub HQ is at Yokosuka (including Submarine Flotilla 2 with about 9 Oyashio and Soryu submarines) and
- at Kure (near US Marines Iwakuni Base) is Submarine Flotilla 1 about 9 Oyashio and Soryu subs)
In a remarkably detailed open source description - the following are excerpts of a Sentaku Magazine's article via The Japan Times, November 26, 2015 http://www.japantimes.co.jp/opinion/2015/11/26/commentary/japan-commentary/japans-crack-submarine-fleet/#.Vle27HYrLb1:
"Japan’s crack submarine fleet
The central headquarters of both the U.S. Navy [Seventh Fleet] in Japan and the [Japanese Navy] are located in Yokosuka, Kanagawa Prefecture, and [the Japanese Navy's] submarines’ operations are effectively integrated with the U.S. Navy.
During the Cold War, the U.S. Navy entirely entrusted to [the Japanese Navy's] submarines the role of watching the movements of Soviet submarines in the Soya Strait between Hokkaido and Sakhalin, the Tsugaru Strait between Honshu and Hokkaido, and the Tsushima Strait between Kyushu and South Korea.
The American reliance on those [Japanese Navy] submarines stemmed from their excellence in small-turn performance [maneuverability]. They are capable of navigating over topographically complicated sea floors with steep uphills, gorges and tangled sea currents in pitch-dark conditions, usually moving at a speed of 5 knots. Today, [the Japanese Navy's] submarines can trace every movement of Chinese naval vessels, including subs, from their port departure to every point of their routes, by utilizing an analysis of information sent from U.S. reconnaissance satellites as well as radio waves.
Before the collapse of the Soviet Union, the [Japanese Navy] had 16 submarines and deployed three each in the Soya, Tsugaru and Tsushima Straits with the remaining seven under repair or engaged in training exercises. Lately though, with the rise of Chinese naval power, many of [the Japanese Navy's] submarines are being shifted to waters around the Nansei (aka Ryukyu) Islands (the island chain between Kyushu and Taiwan). The [Japanese Navy], which now has 18 submarines, plans to raise the number to 22 by 2018.
Critical areas of [the Japanese Navy's] submarine activities aimed at China are the Tsushima Strait, the Miyako Strait between Okinawa Island and Miyako Island, and the Osumi Strait off the southern tip of Kyushu, each of which constitutes a passageway through which Chinese naval vessels must pass to move from the East China Sea to the Pacific Ocean.
…Moreover, [the Japanese Navy's] submarine crew members possess outstanding skills for detecting the position and movement of enemy vessels by analyzing and processing the sounds emanating from them. The subs’ sonar equipment, including a towed array sonar trailing behind a submarine for several hundred meters, has the capability to detect sounds coming from a vessel up to 80 km away.
…Some time ago, Adm. Wu Shengli, commander of the Chinese People’s Liberation Army Navy, told a high-ranking [Japanese] Self-Defense Forces officer that his navy was aiming to become a “blue-water navy,” meaning that it would become capable of operating across the deep waters of open oceans. In the 1990s, China was known to have only a “brown-water navy,” which can operate only in rivers and coastal areas. True to Wu’s words, China has since been endeavoring to expand its areas of operation into the Pacific.
The East China Sea, where [the Japanese Navy's] submarines are deployed, has long stretches of continental shelves, making the average depth only 180 meters, and some areas only 50 meters. That is why China now looks to the South China Sea, where waters are 3,000 to 4,000 meters deep in a number of areas, and has concentrated its state-of-the-art submarines in the South Sea Fleet [with many subs of that fleet based at Sanya/Yulin, in China's Hainan Island].
That has led the Japanese Defense Ministry to keep an eye on the 150-km-wide Bashi Channel [Luzon Strait] between Taiwan and the Philippines, which could be used by Chinese submarines as a gateway to the Pacific, which in turn could rapidly increase confrontation with [the Japanese Navy's] submarines around the [Bonin Islands] and other Japanese islands in the Pacific.
The capabilities of [the Japanese Navy's] submarines today far surpass those of their Chinese counterparts [eg. Yuan class subs]. But [a Japanese naval] officer has warned that if China secretly obtains advanced technologies from various countries and combines them like a jigsaw puzzle, the day may come when Chinese submarines will be on a par with those of [the Japanese Navy]…” See WHOLE ARTICLE
Please connect with Submarine Matters Possible Japanese Submarine Deployment Area, February 20, 2015 which also describes the rising importance of the Bashi Channel (Luzon Strait) as a deployment area.