Japan's maritime history can be traced at least as far back as the first millennium, but the country did not fully emerge as a significant naval power until the Meiji Restoration. As an industrialized nation, Japan relied on maritime commerce to acquire the resources it needed to develop a powerful economy and a navy capable of protecting Japan's all-important sea lines of trade and communication.
Japan's reliance on foreign trade and maritime commerce only grew as Japan emerged as a great economic power in the post-World War II era. The Japanese sea lines of communication are deemed critical security concerns because Tokyo remains reliant on the import of energy, minerals and food, as well as the outward shipment of manufactured goods. In terms of volume, almost all of the country's trade is seaborne. The existence of Japan as we know it depends on these maritime trade routes.
The country's historical record also serves as an acute reminder of its maritime trade vulnerabilities. During the Pacific War, Japan was entirely reliant on sea transport to bring food and resources to the home islands while deploying and resupplying its forces across the Pacific theater. Despite displaying considerable acumen and innovation in a number of different spectrums (including night fighting, carrier operations and amphibious operations), the Japanese navy had a woefully inadequate anti-submarine warfare strategy that was never adequately strengthened during the war.
As a result, submarines — ideally suited for unrestricted warfare against merchant shipping — played havoc with Imperial Japan's sea lines of communication, with U.S. submarines alone accounting for at least 50 percent of Japan's merchant ship losses. The Pacific submarine campaign played a critical role in the defeat of Japan, strangulating Tokyo's supply operations and effectively crippling the Japanese economy.
Having learned its lesson the hard way from World War II, the Japanese Maritime Self-Defense Force made anti-submarine warfare one of its top three priorities during Japan's first formal buildup plan in the postwar era (1958-1960). The other two priorities were the wider protection of Japan's sea lines of communication and the defense of the home islands against a direct invasion from the sea.
Driven by national security concerns and shifts in U.S. policies regarding the Asia-Pacific region (particularly the 1960 Far East clause and Nixon's 1969 Guam Doctrine), the Japanese Maritime Self-Defense Force proceeded over the next few decades to build up a formidable anti-submarine warfare capability — arguably the second-most capable in the world, with a heavy reliance on anti-submarine warships and a large fleet of maritime patrol aircraft. Indeed, the primary mission of the Hyuga-class helicopter carrier, the largest warship class currently in the Japanese naval service, is anti-submarine warfare.
During the Cold War, the Japanese Maritime Self-Defense Force consistently tested its anti-submarine capabilities by tracking Russian Pacific Fleet submarines in the seas of Okhotsk and Japan and by participating in joint training with the U.S. Navy. With North Korea's growing reliance on submarines and with the Chinese navy submarine fleet's explosive growth in capability over the last two decades, the Japanese Maritime Self-Defense Force is going to continue to place great emphasis on its anti-submarine warfare capabilities, even as it seeks to cultivate other previously underdeveloped offensive components, such as amphibious warfare and perhaps even land attack cruise missiles.
Indeed, the core of Japan's future naval military development will continue to be largely centered on anti-submarine warfare. The 25DD class destroyer project is reportedly planned to be optimized for anti-submarine duties, while Japan's helicopter carrier warship fleet — ideally suited for anti-submarine warfare — is to be reinforced in 2015 by two 19,000-ton vessels that will be the largest warships in the history of the postwar Japanese navy. The Japanese Maritime Self-Defense Force is also introducing the Kawasaki P-1 as a successor to the navy's huge fleet of P-3C maritime patrol/anti-submarine aircraft (the second-largest in the world).
However, the P-1 has been plagued by technical problems and delays. As recently as May 13, a P-1 aircraft developed engine trouble, which resulted in the grounding of the aircraft until the problem can be resolved. Previously, wing and fuselage cracks were found during the P-1's development stage that delayed its introduction by a year. Given the critical importance of fielding a replacement to the P-3C and the more general prominence of anti-submarine warfare as a whole, Japan will continue with the P-1 program, as well as other anti-submarine warfare-related programs, to ensure that it maintains a considerable edge in the field well into the future.