Differences in Maritime Traffic Protection Between the Navies of the United Kingdom and Japanese During World War II

Tadashi KOYAMA, a former Navy Captain who participated in the writing of Senshi-Sosho: Maritime Escort Operations, summarized the factors that influenced Imperial Japanese Navy measures concerning maritime escort operations before the outbreak of the war as follows.[19]

• In pre-war Imperial Japanese Navy operational plans, the goal of maritime traffic protection was to secure the Asian waters north of the Taiwan Strait, and the policy was that it would be unavoidable for the Navy to not conduct maritime traffic protection in the South China Sea and the South Seas Mandate if circumstances did not permit. There was no concept of protecting maritime traffic south of the South China Sea in the operational plans drawn up against the United States.
• Pre-war naval armament expansion plans centered on the Asian waters north of the Taiwan Strait, and military armaments to secure traffic south of the South China Sea were not considered in operations against the United States.
• Under an environment of disarmament treaties, the Imperial Japanese Navy was forced to devote all its efforts to developing fleet battle forces, inevitably making the development of enhanced defensive forces (including escort forces) a secondary priority.[20] (In light of the anticipated threat of U-boats, the Royal Navy halted the construction of large ships and prioritized the construction of small anti-submarine vessels such as corvettes. Furthermore, it converted numerous trawlers and equipped them with guns, depth charges, and ASDIC.[21])

As stated above, the reasons why Japan ended up neglecting maritime traffic protection are intertwined with factors originating not only from Japan but also from the United States. On the other hand, considering that the Imperial Japanese Navy thoroughly investigated World War I, and the importance of maritime traffic protection was recognized even within the naval leadership, yet the research findings were not fully utilized, it seems likely that even if Japan had not occupied the Dutch East Indies and had conducted a war focused on protecting the waters north of Taiwan as outlined in pre-war naval operational plans, maritime traffic protection would still have been treated as a secondary concern.

This is because three decisive differences influencing Japanese and U.K. naval operations seem to have collectively contributed to the neglect of maritime escorts. Namely, Japan (1) had not had any tragic experiences deeply ingrained in the memories of its people in any wars since the Meiji era, (2) had an attachment to the successful experience of winning naval battles in the First Sino-Japanese War and the Russo-Japanese War through decisive battles involving capital ships, and (3) underestimated the submarine threat.

For Japan, modern warfare since the Meiji era (the First Sino-Japanese War and the Russo-Japanese War) were also battles of modern navies.

In the First Sino-Japanese War, the Imperial Japanese Navy played a role in transporting army forces to the Korean Peninsula. Fearing an effect on trade with neutral countries such as the United Kingdom, it avoided attacking Qing merchant ships by keeping Shanghai, a supply base for the Qing army and a center of British commercial activity, outside the combat zone.[24] The Qing Navy, on the other hand, possessed the modern Beiyang Fleet, but its coordination among fleets was poor, and it did not target Japan’s vulnerability, namely its supply lines, particularly troop transport ships.[25]

In the Russo-Japanese War, to compensate for its disadvantage in capabilities, the Russian Far East Fleet focused its major strategic objective on preventing the transport of military supplies from Japan to Korea until the arrival of the Baltic Fleet. As a result, the Russian Navy captured or sank dozens of Japanese transport ships, as well as many merchant ships from “neutral” countries such as the United Kingdom, Germany, and the United States, cutting off the supply of food, firearms, ammunition, and important railway materials to Manchuria. However, due to the Qing government’s neutrality policy, Russia could not use Chinese ports as a base for attacks, and after its major ships were heavily damaged in August 1904, the Russian Far East Fleet almost never left Vladivostok until the end of the war,[26] so the commerce raiding lacked thoroughness.

Commerce raiding is warfare aimed at crushing the will to continue fighting among the target country’s people, and it takes a long time for its effects to become apparent. If Japan had learned from the United Kingdom in World War I, it should have been prepared for a long war from the beginning, but the Imperial Japanese Navy only mentioned the possibility that a war against the United Kingdom and the United States might become a long war at an Imperial Conference just before the outbreak of war (September 6, 1941).[27] Furthermore, the time when Japan actually became serious about maritime traffic protection was only when the second phase of operations (the defense of the occupied Dutch East Indies) began, and the U.S. Navy started unrestricted submarine warfare in earnest, causing a dramatic increase in damage to ships.

Taiwan has two geopolitical vulnerabilities. The first is its high dependence on overseas resources, which is the same as for Japan and the United Kingdom.

Taiwan’s energy self-sufficiency ratio (2024) is low at approximately 4.2%. While there has been a slight improvement due to a gradual decrease in domestic electricity consumption and an increase in the supply of renewable energy (solar, wind, etc.), there is no possibility of a significant improvement.[28] The structure relying on imported energy for approximately 83% of electricity generation (coal 35.4%, LNG 47.8%) continues, and although renewable energy is compensating for the shutdown of nuclear power plants in May 2025 under the Democratic Progressive Party administration’s nuclear phase-out policy, solar and wind power account for 83% of this, meaning it does not constitute a stable supply source.[29]

According to calculations by the Ministry of Agriculture (MOA), Executive Yuan, Taiwan’s food self-sufficiency ratio in 2023 was 30.3%, the lowest in the past 10 years, due to drought and other factors. Recently, the food self-sufficiency ratio has been on a downward trend since its peak of 34.7% in 2018.[30] Although Taiwan boasts high self-sufficiency ratios for domestic chicken and pork production, it relies on imported grains and feed, so these figures could potentially push down Taiwan’s actual self-sufficiency ratio.[31] For Taiwan, its low self-sufficiency ratios in both energy resources and food constitute “twin vulnerabilities.”

The second vulnerability is that Taiwan’s economic structure is excessively dependent on semiconductor production.

Taiwan’s semiconductor industry generates TWD 4.3 trillion in production value, accounting for 18% of GDP and 60% of total exports, so a downturn in the semiconductor industry directly translates to a downturn in the Taiwanese economy. Furthermore, the semiconductor industry is highly dependent on electricity, and industrial-use electricity accounted for 55.2% of electricity demand in Taiwan in 2024,[32] ten percentage points higher than in Japan (45.4%).[33] The Taiwan Semiconductor Manufacturing Company (TSMC) alone consumed approximately 9% of the total power consumption in Taiwan,[34] and it has been pointed out that this figure could rise to 24% by 2030.[35] Therefore, if the import of energy resources were disrupted in the event of a Taiwan contingency, semiconductor production would be immediately affected, so we can conclude that the energy self-sufficiency ratio and the semiconductor industry are linked vulnerabilities. Moreover, the major raw materials necessary for Taiwan’s semiconductor manufacturing are mainly imported from suppliers in Japan, the United States, the Republic of Korea, and Europe; and if these imports were delayed, then production would immediately be disrupted in a similar way.

On the other hand, Taiwan’s semiconductor industry can also be seen as a deterrent against a Taiwan contingency. Taiwan manufactures over 60% of the world’s semiconductors and approximately 90% of the cutting-edge chips used in AI, smartphones, data centers, and military systems.[36] Taiwan far surpasses the Republic of Korea, China, and the United States, and TSMC, in particular, has approximately 500 customers in the global semiconductor industry who cannot function without its support.[37] China also greatly depends on Taiwanese high-end semiconductors. However, if China strengthens its own semiconductor industry and reduces its dependence on Taiwan, it could potentially use this to its advantage. For example, there is a scenario under which China could use imports of energy resources and semiconductor materials as a means of blackmail to shock the Taiwanese and global economies, forcing concessions from Taiwan. In this sense, excessive strength in the semiconductor industry is a double-edged sword for Taiwan.

The Republic of China (Taiwan) was established on the Chinese mainland in 1912 and the Presidential Office was moved to Taipei in December 1949 following the Chinese Civil War. Since then, Taiwan and China have repeatedly clashed across the Taiwan Strait, resulting in three crises (the Taiwan Strait Crises) to date.

The first crisis occurred in September 1954, when China, aiming for the reunification of Taiwan, shelled Kinmen Island and seized Dachen Island, pushing Taiwan back to its main islands, including Kinmen and the Matsu Islands. The crisis continued for approximately a year, ending when Taiwan abandoned its base in Zhejiang Province. (The shelling of Kinmen and Matsu Islands continued until 1978.) The second crisis began in August 1958 when China again shelled Kinmen Island and the U.S. Navy dispatched the 7th Fleet to support Taiwan, with the crisis effectively ending two months later in October. The third crisis continued for about two years, starting in 1995. In June of the same year, President Lee Teng-hui visited the United States to give a lecture at his alma mater, Cornell University. As predictions emerged that Lee Teng-hui would win the legislative elections (December 1995) and the Taiwanese presidential election (March 1996), China conducted missile launch exercises and military exercises around the Taiwan Strait in late July 1995. In March 1996, just before the Taiwanese presidential election was held, the Chinese military again conducted intensive military exercises, including missile launches, near the Taiwan Strait. Concerned that stability in the Taiwan Strait would be disrupted, the United States responded by dispatching two aircraft carrier task forces to the waters off Taiwan, and the crisis ended.

As described above, all security situations involving the use of force that Taiwan has experienced have ended on its outlying islands and surrounding waters, and no military damage has ever extended to the main island of Taiwan. Furthermore, all of these incidents were resolved through military intervention by the United States. In other words, in its approximately 80-year history since the relocation of its capital in 1949, Taiwan has never experienced total war, nor has it experienced a war where its people faced starvation. The image of a Taiwan contingency in the minds of the Taiwanese government and people is, in a sense, optimistic, similar to that of the Japanese government and people before the war against the United Kingdom and the United States. There is likely an expectation that the United States would intervene if war broke out. This was clear in a survey conducted by the Center for Strategic & International Studies (CSIS) of U.S. and Taiwan security experts (January 2024), in which more than 70% of the Taiwan experts responded that the United States would intervene militarily if China were to militarily blockade or invade the main island of Taiwan.[38]

In recent years, discussions on a Taiwan contingency have focused on scenarios in which China isolates Taiwan from the outside world in some way. For example, Robert Blackwill and Philip Zelikow of the U.S. Council on Foreign Relations examined a scenario in which China quarantines Taiwan under domestic law, offering the prospect of relatively manageable risks and high rewards. Furthermore, they analyzed that China would not only demonstrate meaningful sovereignty; it would gain the military benefit of effectively blocking the further military modernization of Taiwan’s defenses, possibly permanently. China would declare control over Taiwan’s airspace, run effectively a clearance operation offshore or in the air to screen incoming ships and aircraft, and halt logistics.[39] The aforementioned CSIS survey also showed that 63% of Taiwan experts believe China has the capability to quarantine the Taiwanese military through law enforcement, and 60% believe it has the capability to impose a blockade militarily. Furthermore, a former Chief of the General Staff of the Taiwanese military, Lee Hsi-min, also stated that quarantine and blockade are low-cost and can be expected to be highly effective, and that China is more likely to choose quarantine, which has a lower likelihood of escalation to military conflict.[40]

However, it would take a long time for a quarantine and blockade of the main island of Taiwan to be effective. Furthermore, even in law enforcement, seeking immediate results carries the risk of escalation to the use of force, and if the desired effect is not achieved due to resistance from Taiwan, there is a possibility of escalation to higher military measures. The fact that Germany’s commerce raiding in the two world wars gradually escalated into illegal attacks and eventually unrestricted submarine warfare when it was thwarted by the response from the U.K. military shows an actual example of the interaction universally inherent in warfare.

Needless to say, for Taiwan to withstand a Taiwan contingency and maintain the status quo, it must implement domestic measures to mitigate its own geopolitical vulnerabilities before a contingency begins. Nuclear power plants should be restarted and new ones constructed to improve the energy self-sufficiency ratio, but there are currently no concrete plans to do so.[41]