Abstract
This paper traces the intricate history of Mitsubishi Heavy Industries (MHI) as a premier builder of submarines, a role that has positioned it at the nexus of Japanese industrial policy, naval strategy, and technological innovation for over a century. The analysis begins with Mitsubishi’s foundational contributions to the Imperial Japanese Navy (IJN), examining its role in assimilating foreign technology and scaling up domestic production capabilities. It then navigates the complex post-war hiatus, detailing the company’s resurgence as the central pillar of Japan’s Maritime Self-Defense Force (JMSDF) submarine fleet during the Cold War. The paper critically assesses the technological trajectory from licensed builds to entirely indigenous, world-leading designs, epitomized by the Sōryū and Taigei-classes. Finally, it considers the contemporary challenges and strategic opportunities facing Mitsubishi’s submarine division, including Japan’s re-emergence as a strategic arms exporter, the intensifying technological competition in the undersea domain, and the implications of the Australia-Japan-United States strategic partnership. By situating Mitsubishi’s submarine enterprise within broader historical and geopolitical contexts, this paper argues that the company has been, and remains, an indispensable agent of Japanese maritime power, whose future is inextricably linked to the nation’s evolving security posture.
Introduction
The submarine represents one of the most complex and strategically significant artifacts of modern industrial-military endeavour. Its development demands the seamless integration of advanced metallurgy, precision engineering, acoustic science, weapons control, and human factors—a challenge that has historically been met by only a handful of elite shipyards worldwide. Among this select group, Mitsubishi Heavy Industries (MHI) stands out not only for its longevity and technical achievements but also for its unique trajectory, which mirrors Japan’s own turbulent journey from aspiring imperial power to pacifist nation and, more recently, to a proactive contributor to international security. The story of Mitsubishi submarines is more than a corporate history; it is a lens through which to examine a century of Japanese technological aspiration, naval strategy, and the intricate relationship between the state and private industry.
This paper posits that Mitsubishi’s submarine division has consistently served as a national strategic asset, its fortunes waxing and waning with Japan’s geopolitical circumstances. Its development can be segmented into four distinct, albeit overlapping, phases: the Imperial Foundation (1904-1945), characterized by technology transfer and rapid industrial mobilization; the Post-War Hiatus and Rebirth (1945-1970), a period of constitutional constraint followed by rearmament under the U.S. security umbrella; the Era of Indigenous Mastery (1970-2009), marked by the transition from licensed production to bespoke, world-class designs; and the Contemporary Strategic Pivot (2009-Present), defined by technological leaps in air-independent propulsion (AIP), the abolition of the arms export ban, and forays into the international market. By analysing each phase in turn, this paper will demonstrate how MHI has cultivated a deep-seated culture of engineering excellence and systemic integration, enabling it to produce some of the quietest and most capable conventional submarines in the world today. The conclusion will project this trajectory forward, considering the formidable challenges and unprecedented opportunities that will define the future of Mitsubishi’s underwater enterprise.
1. The Imperial Foundation: Forging the Underwater Armada (1904-1945)
The genesis of Japanese submarine capability lies in the Meiji Restoration’s determined drive to modernize and avoid the colonial fate that had befallen its Asian neighbours. Recognizing the naval supremacy of Western powers, Japan embarked on an aggressive program of technology acquisition. Mitsubishi, founded as a shipping firm by Iwasaki Yatarō in 1870, had rapidly diversified into heavy industry, establishing the Nagasaki Shipyard in 1857, which would become the cradle of Japanese naval engineering (Samuels, 1994).
Japan’s first submarines were not built domestically but purchased abroad. The Imperial Japanese Navy acquired its first five Holland-type submarines from the United States in 1904, which were assembled at the Yokosuka Naval Arsenal (Carpenter & Polmar, 1986). However, the strategic imperative for a domestic construction capability was clear. Mitsubishi, alongside its rival Kawasaki Shipbuilding Corporation, was tasked with mastering this new technology. The first significant milestone was the launch of Holland No. 6 at the Yokosuka Arsenal in 1905, but domestic construction soon followed. Mitsubishi’s Kobe Shipyard delivered its first submarine, the No. 6 (a modified Holland-type), in 1906, marking the true beginning of Japan’s indigenous submarine industry (Jentschura, Jung, & Mickel, 1977).
The interwar period saw a voracious and systematic campaign of technological assimilation. Japanese naval missions were dispatched to Europe, studying British, German, and Italian designs. This led to a series of licensed builds and subsequent indigenous developments. A pivotal moment was the acquisition of technology from Germany following World War I. As a consequence of the Treaty of Versailles, Germany was forced to surrender U-boats to the Allies; Japan received several as war reparations. These U-boats, particularly the U-125 and others of the UE II and UB III types, were subjected to intense scrutiny and reverse-engineering by the IJN and its industrial partners, including Mitsubishi (Boyd & Yoshida, 1995).
This process fueled an era of remarkable experimentation and diversification. Mitsubishi was at the forefront of constructing a wide array of submarine types for the IJN:
- I-boats (Junsen and Otsu types): Large, long-range submarines designed for fleet reconnaissance and commerce raiding. Mitsubishi built several, including the I-1 and I-2 classes.
- RO-boats (Kai and Shi types): Medium-sized coastal submarines.
- Special Types: This included the infamous I-400-class, built at the Kure Naval Arsenal with components from Mitsubishi and other contractors. These were the largest submarines in the world until the advent of nuclear ballistic missile submarines, designed to carry three Aichi M6A1 Seiran attack aircraft, embodying the IJN’s emphasis on strategic reach and innovation (Sakaida, Nila, & Takaki, 2006).
Mitsubishi’s role was not merely one of fabrication. The company’s engineers worked in close concert with the IJN’s Naval Technical Department to refine and improve upon foreign designs. They developed advanced torpedoes, notably the Type 95, an oxygen-powered weapon derived from the British “Long Lance” surface torpedo, which was superior to its contemporary Allied counterparts in range and stealth (Evans & Peattie, 1997). The shipyards themselves became hubs of innovation in welding, pressure hull construction, and diesel engine design.
However, this period also revealed strategic and doctrinal flaws that would prove fatal. The IJN’s submarine force was primarily integrated into the Mahanian decisive battle doctrine, tasked with scouting and whittling down the American battle fleet before the main engagement. This marginalized the more strategically devastating role of commerce warfare that had been so effectively demonstrated by German U-boats in both World Wars. As historians Boyd and Yoshida (1995) argue, “The Japanese submarine service was a technical success but a doctrinal failure” (p. 78). The boats were often large, complex, and sometimes mechanically unreliable, and their operational employment was frequently misaligned with their capabilities.
By the end of World War II, Mitsubishi had built a significant proportion of the IJN’s formidable submarine fleet. The Nagasaki and Kobe shipyards had been transformed into centres of excellence for underwater warfare technology. Yet, the devastation of war and the subsequent Allied occupation brought this entire industrial edifice to an abrupt halt. Japan’s defeat and the imposition of Article 9 in its new constitution seemingly ended its career as a builder of warships.
2. Post-War Hiatus and Rebirth: The Maritime Self-Defense Force Era (1945-1970)
The seven-year Allied occupation of Japan dismantled its military-industrial complex. Under the Supreme Commander for the Allied Powers (SCAP), shipyards like Mitsubishi were prohibited from warship construction and repurposed for civilian merchant shipbuilding to support economic recovery. The nascent Japan Maritime Safety Agency, established in 1948, was a civilian coast guard-like force.
The geopolitical landscape shifted dramatically with the outbreak of the Korean War in 1950 and the escalation of the Cold War in Asia. The United States now saw a rearmed Japan as a crucial bulwark against Soviet expansionism. The 1951 Security Treaty between Japan and the United States formalized this relationship, and in 1954, the Japan Maritime Self-Defense Force (JMSDF) was established. Its mandate was purely defensive: to protect Japan’s territorial waters and sea lanes against submarine and mine threats, primarily from the Soviet Union (Maeda, 2011).
The rebirth of Mitsubishi’s submarine division was thus a direct consequence of Cold War imperatives. The JMSDF’s initial submarine force was modest, starting with the former U.S. Navy Gato-class submarine, USS Mingo, transferred in 1955 and recommissioned as the JS Kuroshio (SS-501). This provided JMSDF crews with vital operational experience. However, the strategic goal was always the reconstitution of a domestic construction capability.
The first post-war Japanese-designed submarine was the Oyashio (SS-511), launched in 1959. However, recognizing the technological gap that had developed during the post-war years, Japan once again turned to foreign technology. The pivotal decision was to license-build the American Barbel-class design. The Barbel-class was revolutionary, being the first class of submarines to combine a single-hull teardrop form (optimized for underwater speed and quieting) with a centralized combat system (the SUBIC). This was a generational leap from the previous, more traditional designs.
Mitsubishi’s Kobe Shipyard was chosen to build the lead boat of this new class, the JS Uzushio (SS-566), launched in 1970. Kawasaki would build subsequent boats. The Uzushio-class program was a masterclass in technology transfer and assimilation. As naval historian Eric Wertheim (2013) notes, “The introduction of the Uzushio class marked Japan’s re-entry into the front rank of submarine-building nations” (p. 354). Mitsubishi engineers did not simply replicate the American design; they adapted and improved it, incorporating Japanese-made steel for the pressure hull and beginning the process of indigenizing subsystems. This program re-established the critical triangle of collaboration between the JMSDF’s Maritime Staff Office, the Technical Research and Development Institute (TRDI), and the private shipyards—a partnership that remains the bedrock of Japan’s naval procurement to this day.
3. The Era of Indigenous Mastery: From the Yūshio to the Sōryū (1970-2009)
The success of the Uzushio program provided the confidence and technical foundation for Japan to embark on a fully independent submarine development path. The subsequent Yūshio-class (first boat launched by Mitsubishi in 1979) retained the Barbel’s teardrop hull but was entirely a Japanese design. It featured indigenous sonars, combat systems, and torpedoes. This class solidified the JMSDF’s operational doctrine of controlling the strategic straits around the Japanese archipelago to bottle up the Soviet Pacific Fleet—a classic anti-access/area denial (A2/AD) mission.
The Harushio-class that followed in the 1990s continued this trend of incremental improvement, with a focus on advanced quieting technologies. Japan was now closely monitoring global submarine trends, particularly the shift towards anechoic tile coatings to absorb active sonar pulses and dampen internal machinery noise. MHI and Kawasaki developed and applied their own sophisticated anechoic tiles, a process that has become increasingly refined with each successive class.
The culmination of this decades-long process of indigenous development was the Oyashio-class (not to be confused with the 1960s namesake). Launched between 1998 and 2008, the Oyashio-class represented a mature, highly capable, and exceptionally quiet conventional submarine. It integrated a new flank-array sonar system and featured further advancements in quieting, including raft-mounted machinery and skewed propeller designs to reduce cavitation. The Oyashio-class confirmed Japan’s status as a global leader in non-nuclear submarine technology.
However, the true paradigm shift came with the Sōryū-class. Authorized in the early 2000s, the lead boat, JS Sōryū (SS-501), was launched by MHI’s Kobe Shipyard in 2007 and commissioned in 2009. The Sōryū-class was a dramatic leap forward for two primary reasons: its size and its propulsion system.
First, at 4,200 tons submerged displacement, the Sōryū was significantly larger than the Oyashio-class, providing greater endurance, improved habitability, and more space for future weapons and sensor upgrades. Its X-shaped stern plane configuration, a feature more common in Dutch and Swedish designs, offered superior manoeuvrability, particularly in shallow coastal waters.
Second, and most significantly, the first six boats of the class incorporated the Stirling engine-based Air-Independent Propulsion (AIP) system, licensed from the Swedish firm Kockums. AIP allows a conventional submarine to operate without access to atmospheric oxygen for extended periods, dramatically reducing its need to snorkel and thereby increasing its stealth and underwater endurance from a few days to several weeks. The integration of this complex system was a major engineering achievement for MHI. As analysts from the Janes defence group noted at the time, the Sōryū “set a new global benchmark for large, long-endurance conventional submarines” (Scott, 2009).
The Sōryū-class symbolized the complete maturation of Japan’s submarine industry. No longer a follower or a licensed producer, MHI was now an innovator, synthesizing foreign technology with its own deep well of engineering expertise to produce a world-leading product. This indigenous mastery, however, was about to collide with a new set of strategic realities that would force a fundamental reconsideration of Japan’s entire defence industrial policy.
4. The Contemporary Strategic Pivot: AIP, Exports, and the Indo-Pacific (2009-Present)
The 21st century has witnessed a rapidly shifting security environment for Japan. The primary submarine threat has shifted from a diminished Russian Navy to a rapidly modernizing and increasingly assertive Chinese People’s Liberation Army Navy (PLAN), which is building its own submarine fleet at an impressive rate. North Korea’s continued development of ballistic missile submarines also presents a direct threat. In response, the JMSDF has prioritized qualitative superiority over quantitative strength, a strategy that plays directly to MHI’s strengths.
The technological evolution of the Sōryū-class itself tells a story of relentless innovation. Beginning with the seventh boat, JS Ōryū (SS-511), MHI made a momentous switch: it replaced the Stirling AIP system with lithium-ion batteries. This was a bold, world-first application of this technology to a military submarine. Lithium-ion batteries offer a higher power density than the lead-acid batteries used in all previous submarines, allowing for longer submerged high-speed dashes and potentially reducing the need for a separate AIP system altogether. This transition, fully realized in the subsequent Taigei-class (first boat launched by MHI in 2020), demonstrates Japan’s commitment to maintaining a technological edge. The Taigei (meaning “Great Whale”) and its sisters represent the current apex of MHI’s submarine design philosophy: larger, quieter, and powered by a revolutionary energy storage system.
However, the most significant strategic shift for Mitsubishi has been political. For decades, Japan’s self-imposed ban on arms exports, embodied in the “Three Principles on Arms Exports” (1967) and their subsequent tightening (1976), prevented companies like MHI from marketing their defence products internationally. This policy preserved Japan’s post-war pacifist identity but also created a fragile defence industrial base, reliant on small, costly production runs for the JMSDF alone.
The administration of Prime Minister Shinzō Abe systematically dismantled these restrictions. In 2014, the “Three Principles on Transfer of Defense Equipment and Technology” replaced the old ban, creating a legal framework for arms exports under strict conditions. This policy was driven by a clear strategic logic: to strengthen Japan’s defence industry, deepen security alliances, and contribute to “proactive pacifism.”
Mitsubishi’s submarine division was immediately at the centre of this new paradigm. The most prominent case was the competitive bid to provide Australia with its next-generation submarine under the SEA 1000 program. MHI, in a consortium with the Japanese government, offered a custom-built variant of the Sōryū-class. This was a historic opportunity—the potential export of a front-line, complex weapons platform, a direct reflection of the close strategic alignment between Japan, Australia, and the United States. The Japanese bid was technically strong, promising a low-risk, proven design. However, in 2016, the Australian government selected the French Naval Group’s design, a decision later cancelled in favour of a trilateral AUKUS (Australia-United Kingdom-United States) partnership to acquire nuclear-powered submarines.
Despite this setback, the very act of competing marked a revolution for MHI. It forced the traditionally insular company to engage with the complexities of international marketing, technology transfer, and offset agreements. The experience, while ultimately unsuccessful, provided invaluable lessons for future export endeavours.
The strategic rationale for exports remains compelling. As security analyst Christopher Hughes (2015) argues, “Without exports, Japan’s defence industry faces eventual extinction or at least a severe degradation of its capabilities due to the inability to achieve economies of scale” (p. 142). A steady production line for the JMSDF alone is insufficient to maintain a vibrant industrial base. Exports are now seen as a necessity for sustaining the very capability that guarantees Japan’s defence.
Current opportunities for MHI include potential sales of smaller submarines or technology cooperation with like-minded partners in Southeast Asia, such as the Philippines and Vietnam, who are seeking to bolster their own naval capabilities in the face of Chinese pressure. Furthermore, collaboration under the U.S.-Japan alliance is deepening, with discussions on joint development of common components or even unmanned underwater vehicles (UUVs).
Conclusion: Navigating the Deep Future
The history of Mitsubishi submarines is a chronicle of national ambition, technological perseverance, and strategic adaptation. From its origins in the fervent industrialism of the Meiji era to its current position as a guardian of the Indo-Pacific, the company has repeatedly demonstrated an unparalleled capacity to absorb, refine, and ultimately innovate in one of the most demanding engineering fields. The trajectory from the Holland-type boats to the lithium-ion powered Taigei is a testament to a deeply ingrained culture of excellence.
Looking forward, the future of Mitsubishi’s submarine industry will be shaped by three interconnected dynamics.
First, the technological arms race in the undersea domain will only intensify. The proliferation of AIP systems and advanced lithium-ion batteries is levelling the technological playing field among conventional submarine powers. To maintain its edge, MHI must pioneer the next generation of technologies. This likely includes further advancements in propulsion, such as more powerful and safer battery chemistries, as well as the integration of artificial intelligence (AI) for sensor data processing, threat assessment, and vessel management. The development and integration of large-discharge unmanned underwater vehicles (LDUUVs) as force multipliers, launched from and controlled by host submarines, will be a critical area of research, likely in close collaboration with the U.S. Navy.
Second, the strategic and export environment remains both an opportunity and a challenge. The dissolution of the arms export ban has opened a new frontier, but success is not guaranteed. MHI must transform from a dedicated domestic supplier into a nimble international competitor. This requires not only technical prowess but also mastering the political, commercial, and logistical complexities of global defence sales. Building trust, ensuring reliable supply chains, and offering competitive financing will be as important as the performance specifications of the submarines themselves. The strategic alignment of the Quad (Japan, U.S., Australia, India) and other regional partnerships provides a natural political framework for such cooperation.
Finally, the domestic industrial base faces a demographic and economic challenge. Japan’s shrinking population and declining interest in manufacturing careers threaten the skilled workforce essential for submarine construction. MHI will need to invest heavily in automation, robotics, and digital manufacturing (the “shipyard 4.0” concept) to maintain its production efficiency and quality in the face of a diminishing labour pool.
In conclusion, the story of Mitsubishi submarines is far from over. It is entering one of its most consequential chapters. The company stands as a national champion, its shipyards the custodians of a capability that is central to Japan’s security. Having mastered the art of building world-class submarines, its future success will depend on its ability to navigate the equally complex waters of international strategy, technological disruption, and industrial evolution. The silent service of the JMSDF will continue to rely on the products of Kobe and Nagasaki, but the reach and impact of those products may soon extend far beyond Japan’s territorial waters, projecting Japanese technological power and reinforcing a Free and Open Indo-Pacific.
References
Boyd, C., & Yoshida, A. (1995). The Japanese Submarine Force and World War II. Naval Institute Press.
Carpenter, D., & Polmar, N. (1986). Submarines of the Imperial Japanese Navy. Naval Institute Press.
Evans, D. C., & Peattie, M. R. (1997). Kaigun: Strategy, Tactics, and Technology in the Imperial Japanese Navy, 1887-1941. Naval Institute Press.
Hughes, C. W. (2015). Japan’s Foreign and Security Policy Under the ‘Abe Doctrine’: New Dynamism or New Dead End? Palgrave Macmillan.
Jentschura, H., Jung, D., & Mickel, P. (1977). Warships of the Imperial Japanese Navy, 1869-1945. Arms and Armour Press.
Maeda, T. (2011). The Hidden Navy: The History of the Japan Maritime Self-Defense Force. Kōjinsha. (In Japanese).
Samuels, R. J. (1994). “Rich Nation, Strong Army”: National Security and the Technological Transformation of Japan. Cornell University Press.
Sakaida, H., Nila, G., & Takaki, K. (2006). I-400: Japan’s Secret Aircraft-Carrying Strike Submarine. Hikoki Publications.
Scott, R. (2009, December 16). Japan commissions Soryu submarine. Janes Navy International.
Wertheim, E. (2013). The Naval Institute Guide to Combat Fleets of the World, 16th Edition: Their Ships, Aircraft, and Systems. Naval Institute Press.
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