The Invasion That Never Was

On 26 July 1944, President Franklin Roosevelt posed for a photograph with Admiral Chester Nimitz and General Douglas MacArthur at his side. The three had gathered in Pearl Harbor, Hawaii, for a strategy conference that would determine the direction of the fight against Japan in the Pacific theater. Undeterred by the Hawaii heat, MacArthur wore his characteristic leather flight jacket and seethed at having to leave his area of command for the first time during the course of the war for what he perceived to be a political stunt ahead of the 1944 Presidential elections.¹

Beyond these surface-level complaints, MacArthur was more concerned about the prospect of Operation Causeway, whose strongest advocate was Admiral Ernest J. King. The plan was a proposed invasion of Formosa—now called Taiwan—as the best strategic course to defeat Japan.

MacArthur, on the other hand, believed that the United States was duty-bound to fulfill his promise of returning to liberate the Philippines at the earliest opportunity. Roosevelt played the role of arbitrator, while the two military counterparts argued about the best possible course. In the end, Operation Causeway was rejected—but the plans prepared for the invasion contain valuable lessons that can be applied to the U.S. Navy’s contemporary strategic concerns in the South China Sea. 

Dueling Options

The photographs of General Douglas MacArthur striding through the surf along with his troops to retake the Philippine Islands are well known. However, many remain unaware of the inter-service debate that preceded the invasion of the Philippines, or the strategic alternative that could have averted the need to take control of the islands one-by-one. The Navy advocated for the invasion of Formosa as the superior strategic course, while the Army emphasized the perils of invading such a large island and the possibility of Formosa being bypassed altogether through control of the Philippines. These strategic viewpoints were honed and developed at the Quadrant Conference (August 1943), the aforementioned Roosevelt-MacArthur-Nimitz conference (July 1944), and the Octagon Conference (September 1944).

Admiral King was the clearest voice in support of an invasion of Formosa. King’s position is most succinctly summarized by Craig L. Symonds in World War II At Sea: “King believed that seizing Formosa would cut Japan off entirely from her essential imports and starve her into surrender, making an invasion of the home islands unnecessary.”² Beyond Japan itself, King believed that control of Formosa would “strangulate” the smaller islands, forcing the Japanese occupation to “ultimately perish.”³

On a more practical level, King believed that an invasion of a single island, even if comparatively large, was an easier operational task than neutralizing the approximately 7,000 islands that comprised the Philippines.⁴ He also viewed Formosa as a promising base for long-range B-29 bombers to carry out their attacks against Japan. The minutes of the Quadrant Conference—a conference that included Roosevelt, British Prime Minister Winston Churchill, and top representatives of the Allied armed forces—reveal the guiding assumptions that led King to support a Formosa invasion. First, it was assumed that “air bombardment…is probably an essential prelude to bring about the defeat of Japan.”

On the other hand, planners believed that “to bring about the sustained air offensive against Japan we shall almost certainly require the use of China and/or Formosa as the bases for our long range bombardment.”⁵ This demonstrates how Formosa came to be viewed as a vital hub of Allied bombing. Finally, Formosa was viewed as a critical method of establishing a link to resupply the Chinese forces battling Japanese imperial advances on the Chinese mainland. As late as the Combined Chiefs of Staff meeting on 14 September 1944, Admiral King still clung to a Formosa invasion. When queried by the British Chiefs of Staff over how their naval forces would be utilized in the Pacific, the meeting minutes reveal that King was “in no position now to commit himself as to where the British Fleet could be employed.”⁶ Nonetheless, as Walter Muir Whitehill put it, the Navy was still prepared for a “hard struggle” because of strengthened Japanese reinforcements on the island. The plan was not perfect, but the Navy believed it to be preferable to the Army’s alternative.

For his part, General MacArthur was the most vocal opponent of Operation Causeway. For him, moral and parochial factors weighed as heavily as strategic concerns. First, he believed it was a moral imperative to liberate the Philippines. After serving as Military Advisor to the Philippines, MacArthur had become deeply attached to the Filipino people and gave them a personal promise that he would return after escaping in the face of the Japanese advance. He was intent on living up to his commitment. Moreover, MacArthur felt responsible for the American prisoners of war who were still held captive by the Japanese military.⁷ Additionally, MacArthur was zealous in defense of what he believed to be the Army’s turf. He believed that an invasion of Formosa would yield too much ground to the Navy, making his theater a side show.⁸ As Robert Ross Smith writes, “MacArthur believed that the plans to bypass [the Philippines] were purely Navy-inspired.”⁹

Finally, MacArthur viewed prioritizing the Philippines as strategically more sensible. As Smith puts it, “He declared that the Allies would need to reoccupy the entire Philippine Archipelago before they could completely sever Japan’s lines of communication to the south.”¹⁰ This would save lives and preserve resources. In the end, MacArthur’s argument carried the day because it spanned across the domains of politics, morality, and strategy. MacArthur played three-dimensional chess, while the Navy confined itself to strategic concerns. This proved persuasive.

In the July 1944 conference that took place in Hawaii between Roosevelt, MacArthur, and Nimitz, the President determined not to make a final decision. Instead, he left the choice to the Joint Chiefs of Staff. In October 1944, a JCS directive formally endorsed an invasion of the Philippines, paving the way for MacArthur’s favored island-hopping approach.

Causeway’s Takeaways

Even though the invasion of Formosa was shelved, the Allied preparations contain valuable lessons for contemporary strategy across the Taiwan Strait. Planning for Operation Causeway was developed in a report entitled “Causeway Joint Staff Study” and dated 23 August 1944. The study was completed by the Pacific Fleet headquarters of Admiral Nimitz. Now entirely declassified, the report contains nearly 100 pages of detailed military planning and analysis that reveal highly relevant lessons for the challenges faced by the U.S. Navy today.

Distance: Distance is one of the first considerations discussed by Allied planners in the “Causeway Joint Staff Study.” The planners recorded the precise number of days required to travel the exact number of nautical miles that separated Formosa from key cities. San Francisco, for example, was 5,741 nautical miles from Formosa, requiring 24 travel days. Guam, on the other hand, was 1,500 nautical miles away and would take 6.2 travel days.¹¹ These sheer distances underscored the logistical challenges in making the invasion possible. For example, the report estimated that 9,800,000 barrels of oil would be required for the month of February alone.¹² As a result, planners concluded: “Due to the distance of the objectives from established fleet bases, reliance must be placed on fleet supply and ammunition ships, oilers and floating repair facilities to effect resupply.”¹³ However, on an even deeper level, the discussion of distance implied a Japanese logistical advantage in defending Formosa.

In a potential future conflict over Taiwan, the People’s Republic of China’s (PRC’s) relative proximity to the island of Taiwan means that it would hold the same edge that Japan maintained during World War II. It is important to note, however, that the PRC has pursued measures that continue to strengthen their geographic advantage. In its quest to establish anti-access/area denial (A2/AD) within the First and Second Island Chains, the PRC has built artificial islands and militarized their Coast Guard to make the factor of distance an even greater imbalance in the strategic equation over Taiwan.

The PRC practice of building islands in the South China Sea through artificial means poses both an economic and military concern. On the one hand, greater territory in critical economic sea lanes offers more leverage to disrupt shipping and supply chains. However, the concern is broader than this. In Sea Power, retired Admiral James Stavridis refers to these islands as “unsinkable aircraft carriers” that have “created nearly three thousand acres of land out of the ocean.” Stavridis concludes that these artificial islands “shift the balance between the competing militaries” in the South China Sea.¹⁴

This means that the PRC is pushing its geographic influence ever-closer to Taiwan, while leaving open the option for military escalation. In his 2018 Senate confirmation hearings, Admiral Phil Davidson argued that “the only thing lacking are the deployed forces. Once occupied, China will be able to extend its influence thousands of miles to the south and project power deep into Oceania.”¹⁵ This presents a concern because the already existing barrier of distance facing the United States in aiding Taiwan’s defense becomes even greater.

Another way that the PRC has weaponized its distance advantage is through the militarization of the PRC Coast Guard. Beginning in 2013, the PRC has been repurposing its coastal defense forces. As Ryan D. Martinson writes in a volume edited by Andrew S. Erickson, “China’s expansion in maritime East Asia has relied heavily on non-naval elements of sea power, above all white-hulled constabulary forces.”¹⁶ These forces are organized into the China Maritime Police, China Marine Surveillance, and China Fisheries Law and have been used to enforce Chinese economic interests and territorial claims.

There is also concern that these forces are becoming increasingly militarized. The China Maritime Police, for example, operates several People’s Liberation Army Navy (PLAN) frigates, extending the reach of these regional forces. These developments in Chinese maritime defense forces threaten to extend the PRC’s region of geographic advantage, making it more difficult for the United States to aid in the defense of Taiwan.

The key to countering this geographic advantage is by leaning into the partnership with Taiwan. It is crucial that Taiwan receive the military equipment and material required to deter Chinese aggression so that a situation where China could leverage its geographic advantage is averted.

Sea and Air Superiority: In the 1944 JCS report, Allied planners were certain that sea and air superiority were prerequisites for neutralizing the island of Formosa. Under “Concept of Operations,” they wrote: “The capture and occupation of Formosa . . . requires that our forces establish undisputed control of the sea and air in the area of the operations concerned.¹⁷ The first and second phases of operations constituted “intensive attacks by carrier aviation” and “bombardment by naval gunfire in preparation for the assault.”¹⁸ Of utmost importance was “utilizing strong fast carrier groups to exploit to the fullest every opportunity to engage and destroy the enemy fleet or surface forces.”¹⁹ It is clear that the planners were preparing for the invasion with the assurance of naval superiority; by 1944, it was clear that U.S. naval power was dominant over the Japanese.

However, the contemporary balance of naval power in the South China Sea is not as clear. For several decades, the PLAN has been investing in disruptive technologies that exploit the vulnerabilities inherent in the dominant U.S. Navy. As an example, the PRC has been investing in an arm of the PLA called the Second Artillery, which is dedicated to equipping nearly every platform in the PLAN, including surface ships, submarines, aircraft, and land installations with supersonic and hypersonic cruise missiles.²⁰ This poses a threat because of the damage that can be inflicted on U.S. surface and air targets at relatively low cost. YJ-18, for instance, can travel just 15 feet above the water with a range of 336 miles and has the ability to either sink or cripple an 8,000- to 10,000-ton warship.²¹

In November 2021, the PLAN tested two hypersonic missiles that fly at five times the speed of sound. General Mark Milley, Chairman of the Joint Chiefs of Staff, stated that this was “very close” to a “Sputnik moment,” raising concern that the United States lags behind the PRC in hypersonic development and in defenses to hypersonics.²² These weapons are dangerous not just because of their high speed and low cost, but also because they can be produced at a faster rate than conventional naval forces.

While the Allied navies enjoyed military supremacy by the end of 1944, the current balance of naval forces in the South China Sea is in greater doubt. On the one hand, this strengthens the idea of deterrents, since the PRC would have to establish sea and air supremacy to assure a successful invasion of Taiwan. However, this also raises concerns because disruptive Chinese technologies threaten to establish A2/AD in the South China Sea.

Other Lessons: The 1944 JCS report brings up other concerns that are relevant to potential future conflict across the Taiwan Strait. First, it contains an analysis of the terrain on the island of Taiwan. The report describes the mountainous terrain that makes up much of Taiwan and details that only 20 percent of the island is below 1,600 feet in elevation.²³ These same geographic concerns that would have hampered an Allied invasion in 1944 would also provide natural geographic defenses for the Taiwanese. Here again, it is possible that if tensions were to continue to escalate between the PRC and Taiwan, the PLA would adopt a blockading strategy. In fact, after the visit by then-U.S. House Speaker Nancy Pelosi, some analysts believed that the PLAN’s military exercises were a trial run for a blockade of Taiwan. Just as Formosa was bypassed during World War II, it is also possible that a blockade could achieve the PRC’s political aims without the need for an invasion.

Conclusion

Admiral King’s attempts to prioritize an invasion of Formosa were ultimately unsuccessful. In the end, Formosa was bypassed altogether, not only by MacArthur’s island-hopping campaign, but also through the use of the atomic bombs on Hiroshima and Nagasaki. Nonetheless, the Causeway Joint Staff Study provides lessons that remain relevant for the current tensions that exist between the PRC and Taiwan across the Taiwan Strait. The allied concern about distance between the United States and Formosa remains a challenge that has been compounded by aggressive Chinese strategies such as island building and militarization of the Chinese coast guard. The U.S. Navy air and sea superiority—equally relevant in 2024 as 1944—is in doubt because of disruptive Chinese technologies that exploit the vulnerabilities inherent in conventional naval forces. Even still, the possibility of bypassing an invasion of Taiwan altogether through use of a naval blockade should not be overlooked. To address these challenges, the US Navy should turn to history. Learning the lessons of Operation Causeway could help the Navy to achieve its current strategic objectives.