일본의 잠수함 산업 인프라; 업그레이드하지 말고 짧게 쓰고 새로 만들자!

[위종민]

일본은 미쓰비시 중공업과 가와사키 중공업이 각각 2년에 한 척씩 잠수함을 건조하며, 매년 3월 (1996년과 2014년 제외) 신조함을 인도한다고 합니다. 또 MLU 등을 거쳐 30년씩 쓰는 타국에 비해, 30년을 쓸 수 있지만 그 전에 일정 기간만 운용한 뒤에 퇴역시키거나 훈련함으로 전용한다고 하네요. 퇴역시켜도 당장 해체하거나 유지보수를 중단하는 게 아니라 수 년 동안 일정 정도의 정비를 받는 예비함으로 유지한다고 합니다. 

정기적인 신조함 건조로 잠수함 건조중에 차기 잠수함 설계를 진행할 수 있으며, AIP 등 신기술을 도입할 시 기존 잠수함을 테스트베드로 활용 가능하다고 합니다. (하루시오급 JS 아사시오에 스털링엔진 AIP 모듈 장착, 소류급 JS 오류와 JS 도류에 리튬이온 배터리팩 장착 등) 

또한 해양전략에 따른 잠수함 보유 목표에 따라 일정기간만 운용하고 퇴역시키기 때문에 1980년~2018년 사이엔 18척 보유 목표에 따라 18년만 운용하고 잠수함을 퇴역시켰고, 2019년 잠수함 보유량을 2022년으로 상향시키자 퇴역 연차를 18년에서 2022년으로 상향시켰다고 하네요. MLU 등 중수리는 어떤 문제가 생길 지 예측하기도 어렵고 일정 연장의 위험이 있다고 합니다. MLU는 평시에 비용을 아낄 수 있지만 신조 중심의 현재 산업 생태계가 잠수함 산업 기반을 더 안정적으로 유지할 수 있다고 평가하네요. 

또한 퇴역 이후에도 일정 기간을 예비함으로 유지함에 따라 건조 일정을 앞당기지 않고도 긴급시 해자대는 최대 4척의 작전용 잠수함을 추가로 확보할 수 있다고 합니다. 

https://cimsec.org/japans-submarine-industrial-base-and-infrastructure-unique-and-stable/

Japan’s Submarine Industrial Base and Infrastructure – Unique and Stable | Center for International Maritime Security

SHIPBUILDING

JAPAN’S SUBMARINE INDUSTRIAL BASE AND INFRASTRUCTURE – UNIQUE AND STABLE

JULY 15, 2024 GUEST AUTHOR 1 COMMENT

By Jeong Soo “Gary” Kim

The Japan Maritime Self Defense Force (JMSDF) possesses a modern and highly capable fleet, including light carriers, large AEGIS destroyers, and advanced conventional submarines which are renowned for their size and stealth. While individual Japanese naval vessels and their crews are certainly world class, Japan’s unique approach to naval industrial base strategy is often underappreciated, especially its submarine industrial base. This approach relies on three deliberate policy pillars:

• Ensuring an extraordinarily stable production system for new boats,
• Decommissioning operational boats with plenty of service life left in them, and
• Maintaining these retired submarines in training and ready reserve fleets.

This industrial policy admirably balances cost, readiness, and wartime surge capacity. 

Pillar 1: Stable Production Capacity

The JMSDF received its first submarine, the JS Kuroshio (ex-USS Mingo) as Foreign Military Aid in 1955. Soon after, the JMSDF started ordering domestically produced submarines based on both Imperial Japanese Navy and U.S. Navy designs. Starting in 1965, the JMSDF consistently built ocean-going fleet submarines, and by 1980 starting with the Yushio-class of submarines, Japan had established an incredibly stable submarine industrial base. Mitsubishi Heavy Industries and Kawasaki Heavy Industry’s shipyards in Kobe each produce one boat every two years. With the exception of 1996 (due to the great Kobe earthquake of 1995) and 2014, Kawasaki or Mitsubishi has delivered a submarine on March of every single year like clockwork. This production scheme has held steady through the massive expansion of the Soviet Navy during the 1980s, the peace dividend era of the 1990s and 2000s, and even through the PLA Navy’s surge in the 2010s and 2020s.

Another stabilizing leg of the JMDSF’s submarine industrial base is the forward-looking and well institutionalized research and development scheme. For example, detailed design for the current Taigei-class of submarines kicked off in 2004, even before the previous Soryu-class was laid down. Detailed engineering for a follow-on class, including such features as pump jet technology, was already in the works when the JS Taigei entered service in 2022. Furthermore, when the JMSDF implements new technology, like Air Independent Propulsion (AIP) or large lithium battery packs, it inserts these technologies into an existing class of submarines to validate technical maturity. For example, in 2000 the JMSDF retrofitted a conventional, Harushio-class submarine, JS Asashio, with a Sterling-type Air Independent Propulsion (AIP) module to test its effectiveness before applying the technology to the future fleet. Similarly in 2020, Soryu-class submarines JS Oryu and JS Toryu were fitted with large lithium-ion battery packs instead of the Sterling AIP modules in anticipation of the lithium-ion power pack transition in the Taigei-class. 

Apra Harbor, Guam (April 12, 2013) – Japan Maritime Self Defense Force (JMSDF) Soryu-class submarine Hakuryu (SS 503) visits Guam for a scheduled port visit. (U.S. Navy photo by Mass Communication Specialist 1st Class Jeffrey Jay Price/Released)

Pillar 2: Unique Utilization Strategy at the Operator Level

The JMSDF’s submarine utilization system is unique and may seem odd to American and other Western Navies. While Japanese submarines are well-built and likely could serve as long as their American counterparts (35-40 years), they serve around 18 years before being decommissioned or transferred to training status. While most navies try to sustain submarines as long as economically feasible, the JMSDF “prunes” serviceable submarines out of its operational fleet in order to maintain the number of boats required in Japan’s maritime strategy. For example, between 1980 and 2018, the national strategy called for 18 submarines in the operational fleet, therefore most submarines were decommissioned between the 17-20 years of service to achieve this fleet goal. Starting in 2019, in order to match China’s rising naval power (and perhaps to hedge against the U.S. submarine base’s sluggish production increase), Japan’s maritime strategy increased its submarine requirement to 22 submarines in the operational fleet, and the JMSDF raised the “retirement age” of its submarines from 18 to 22 years until annual submarine production rate allowed the fleet size to reach 22. Officers in the JMSDF’s ship repair unit describe maintaining older submarines as “more costly, but not particularly difficult”, implying that if operational needs dictate, they could increase the number of operational submarines without having to increase the production rate.

Figure 1. Historical JMSDF submarine fleet size and average age of fleet. Credit: Author’s work.

Figure 2. Age in which JMSDF submarines were decommissioned. (Author graphic)

Another unique aspect to the Japanese submarine industrial base planning is that submarines typically do not go into an extensive mid-life refit like their American counterparts. JMSDF leaders cite that overhauling older vessels can often be unpredictable and lead to schedule growth, as submarines can be in much worse material condition than anticipated. They admit that conducting a mid-life upgrade could save cost in peacetime, but the current system that prioritizes new construction ensures more stability in the submarine industrial base. On the ground level, JMSDF ship repair officers cite that cutting holes into a pressure hull and then replacing major components in already tightly packed submarine is time consuming, and believe that new submarine construction “delivers more submarine sea power per man-hour worked” than conducting a midlife overhaul. They jokingly called this practice similar to the “Shikinen Sengu”, which is a ritual where one of the most revered Shinto shrines in Japan, Ise Shrine, is traditionally torn down and rebuilt every 20 years.

Pillar 3: Consistent Supply of Reserve Submarines

Another benefit of consistent production and early retirement is the ability to keep several reserve submarines in good material condition on reserve prior to final decommissioning and disposal. Typically, when submarines are decommissioned from the operational fleet, they are transferred to the training squadron and then consistently sail to train and qualify sailors prior to assigning them to operational boats. The training submarine fleet not only helps supplying the operational fleet with sailors already equipped with sea time inside a submarine, but also allows boats to be quickly transferred back to the operational fleet whenever new construction and delayed decommissioning cannot meet requirements. While the JMSDF has yet to recommission a training submarine back to active service, it has transferred older destroyers, the JS Asagiri and JS Yamagiri, from the training fleet back to the operational fleet in 2011/2012 to meet increased operational surface vessel demand. It is not unimaginable that the JMSDF would be willing to use its training submarines in a similar manner during a period of surging demand.

Furthermore, when submarines stop sailing with the training squadron, they stay on a reserve status receiving a certain amount of maintenance until they are finally stricken and disposed of. The number of submarines kept in this status is not well known, but parts are typically not salvaged to sustain other boats for a number of years. If submarine demand were to outstrip operationalizing the training submarines, the reserve boats could possibly be put out back to sea after some period in maintenance. Consequently, the combination of operationalizing the training and reserve submarines could give the JMSDF the ability to surge up to four additional operational submarines without accelerating its build schedule, which would constitute an impressive 20% increase in capability from the current fleet of 22 boats. 

Conclusion

All in all, Japan sustains an advanced, powerful conventional submarine fleet staffed by dedicated, overworked sailors, and supported by a robust, stable shipbuilding industry. Considering how quickly a shipbuilding industrial base atrophies without consistent inflow of new construction orders, the Japanese method of consistent production and fleet size control through early decommissioning may prove to be a viable template that even the U.S. Navy can incorporate into its long-term naval shipbuilding plan.

Jeong Soo “Gary” Kim is a Lieutenant in the U.S. Naval Reserves and currently a student at the Lauder Institute at the Wharton School of the University of Pennsylvania earning an MBA and MA in East Asian studies. He previously served with the Seabees of Naval Mobile Construction Battalion 5, and with NAVFAC Far East in Sasebo, Japan. He graduated from Columbia University with a bachelor’s degree in mechanical engineering and a minor in history.

The author would like to give special thanks to LCDR Hiroshi Kishida of the JMSDF’s Sasebo Ship Repair Facility, and various junior officers serving in Sasebo-based ships for assisting with the research for this article.

References

Dominguez, Gabriel. “Recruitment Issues Undermining Japan’s Military Buildup.” The Japan Times, The Japan Times, 2 Jan. 2023, www.japantimes.co.jp/news/2023/01/02/national/japan-sdf-recruitment-problems/.

Kevork, Chris. “The Revitalization of Japan’s Submarine Industry, From Defeat to Oyashio.” NIDS Journal of Defense and Security, 14, Dec. 2013, 14 Dec. 2013, pp. 71–92.

Ogasawara, Rie. “Observing the Horrible State of JSDF Military Housing through Photos.” ダイヤモンド・オンライン, 27 Sept. 2022, diamond.jp/articles/-/310137?page=2.

Takahashi, Kosuke. “Japan Launches Fourth Taigei-Class Submarine for JMSDF.” Naval News, 17 Oct. 2023, www.navalnews.com/naval-news/2023/10/japan-launches-fourth-taigei-class-submarine-for-jmsdf/.

일본 신형잠수함 타이게이(大鯨)함 진수의 의미 (Implications of the JMSDF’s New Taigei Class of Submarines), Korea Institute for Maritime Strategy, 11 Dec. 2020, kims.or.kr/issubrief/kims-periscope/peri217/.

Featured Image: Launch Ceremony of SS Taigei. (Japanese Ministry of Defense photo)

[백선호]

인력 유지하려면 계속 만들고, 버리고, 만들고, 버리는 식으로 할 수 밖에 없을 것 같습니다. 노트북이나 휴대폰처럼요.

[위종민]

장보고급도 도입된 지 30년이 훌쩍 넘어서 어떻게 됐나 살펴봤더니 초기형 3척은 훈련함으로 전용된다고 하네요. 그 후에 1:1 대체가 가능할 지..