As tensions between China and the West worsen, increasing attention is being paid to Taiwan. In particular, robust debate about how best to defend Taiwan from a Chinese invasion is occurring. A study of past defenses against amphibious invasions published by retired US Marine Theodore Gatchel suggests several lessons for the defense of Taiwan.  Among these is that not all the conventional capabilities often maligned by American analysts may be as ill-suited to Taiwan’s military as is typically argued. Powerful mechanized forces, in particular, appear essential to repelling amphibious invasions.
The air and naval defenses necessary to protect these forces from interdiction, however, are vast and costly. Rather than financially support Taiwan in establishing them, the United States could attempt to persuade Taiwan to embrace asymmetric defense by adopting a policy of strategic clarity, although it would need to weigh the political repercussions of doing so. If neither course is taken, the peril to Taiwan’s safety will continue to rise.
Amphibious Defense in Theory
Gatchel identifies three components of a defense against an amphibious assault: naval defense, defense at the shoreline, and mobile defense.  Naval defense focuses on targeting enemy warships and transports. Shoreline defense relies on fortifications and troops stationed along the coast battling enemy forces as they conduct the landing. A mobile defense relies on troops held in reserve moving to the enemy beachhead after their landing and destroying it in a counterattack.
Each defensive approach has its strengths and weaknesses. Naval defense, for example, offers the prospect of preventing an enemy landing entirely, but is impotent against enemy forces who do manage to land. Shoreline defenses can be extremely tactically formidable, but they are also extremely rigid. They offer no recourse against enemy forces who penetrate the defensive line. The ideal amphibious defense would therefore integrate all three approaches into a comprehensive strategy. In such a strategy, each successive layer would act as a backstop against the failure of the preceding layer.
The historical cases suggest that strategies that include a strong mobile defense have the best chance of success. Mobile defense, in turn, requires strong mechanized forces (i.e., forces strong in tanks, mechanized infantry, and supporting arms such as artillery) that are capable of powerful tactical and operational offensives in service of a strategic defense. These forces offer commanders a great deal of flexibility in responding to an enemy landing, but they must be able to move to the landing site quickly. Furthermore, commanders must rapidly make decisions as to where to commit them. In Gatchel’s words, mobile defenders are “conducting a race with the attacker to build up combat power at the site of the landing.” 
Past Attempts at Amphibious Defense
The Allied landings at Salerno, Italy, during World War II were the closest a defender has come to repelling a major amphibious assault in modern times.  During that battle, the Germans employed a mobile defense strategy augmented with some shoreline and naval defenses. This strategy hinged on mechanized forces stationed throughout Italy converging on the landing site in time to launch a counterattack that would destroy the beachhead before the Allies could consolidate their presence, epitomizing Gatchel’s “race to build up combat power.”
When that counterattack came at Salerno, it caused such havoc that the Allied commander ordered his staff to prepare for a possible evacuation of the beachhead.  It was fought to a standstill, however, as were follow-up attempts.  Ultimately, the Germans were forced to retreat and establish a defensive line further up the Italian peninsula.
The most fatal flaw in the German defense was inadequate concentration of mechanized forces. Early in the battle, the German high command refused to release two panzer divisions stationed in northern Italy for action at Salerno.  The added power of these two divisions may have lent the decisive counterattack the mass and vigor it needed to destroy the beachhead, as the Allied force ashore early in the battle was little more than four divisions strong. 
The German commander, Albert Kesselring, took this lesson to heart. When the Allies landed further north at Anzio, he was able to mass twenty thousand troops against the beachhead on the first day.  This was enough to force a stalemate, but not to defeat the landing. Allied forces advancing from the south eventually relieved the encircled beachhead. After the battles in Italy, the German high command concluded that a mobile defense by concentrated mechanized forces was the best way to defeat a landing.
By 1944, the Japanese had reached similar conclusions to those of the German high command. At Tarawa, a tiny atoll in the Pacific Ocean, they constructed perhaps the densest network of coastal fortifications faced by any landing during the war. Even here, however, the defense failed for want of a counterattack on the critical first day.  Later, at Saipan, the Japanese planned for a hybrid defense of shoreline positions backed by limited armored reserves, like the Germans in Normandy. In part due to unfinished fortifications and inadequate reserves, however, the defenders failed to repulse the landings.  They were forced to fight a delaying battle in hope of intervention from the Japanese fleet, which never came due to a crushing naval defeat at the Battle of the Philippine Sea. 
After Saipan, the Japanese concluded that beach fortifications alone cannot stop a determined landing and that a mobile defense is therefore required.  Japanese anti-landing strategy continued to evolve, however. At Okinawa, the Japanese made extensive use of kamikazes–which can callously be regarded as primitive guided missiles–against the Allied fleet.  This attempt at a naval defense caused horrendous casualties, but also failed to repel the invasion .
In all the above cases, the defenders used various naval defense techniques.  These efforts were not coordinated with the armies ashore, however, and had little impact on the fighting there.  Overall, Axis naval defense proved “more annoying than decisive.”  Gatchel speculates that “Had these elements of a naval defense been employed in a more coordinated manner, however, they might have delayed the landings enough to have made the armored counterattacks ashore more effective.” 
Lessons for the Defense of Taiwan
The case studies above offer many lessons for amphibious defense. They suggest the importance of unified command, coordination of different layers of the defense, and the necessity of creating a defensive doctrine specific to amphibious operations.  They offer lessons as to how each defensive approach must be executed in order to be successful, and show the capacity of air and naval power to cripple enemy forces ashore. An underappreciated lesson for the current debate about Taiwan’s defense, however, is that a mobile defense is an essential component of any strategy to repel a hostile landing.
This conclusion is supported by the historical record and the conclusions of the defenders themselves. Naval defenses have proven unable to prevent enemy forces from making landfall when that enemy has naval superiority, as China does against Taiwan. They can delay the landing and weaken the enemy force, but relying exclusively on naval defenses to stop an invasion would make for a brittle strategy. Similarly, coastal defenses have proven extremely capable at slowing the enemy advance and inflicting casualties on attackers, but have proven just as incapable of defeating an invasion outright. For any defender that intends to repel a landing, a mobile defense by powerful mechanized forces appears to be an essential backstop to naval and shoreline defenses.
Analysts who argue that conventional capabilities are not suited to Taiwan generally say so because they believe that Taiwan cannot and should not attempt to repel a landing. Some suggest that Taiwan should not attempt a mobile defense because Chinese bombardment will make it impossible, as Allied airstrikes and naval gunfire did during World War II. To prevent such interdiction, Taiwan’s military requires extremely robust air, naval, and other defenses, of the kind that American analysts often advocate for. An approach to coastal defense that eschews mobile forces and invests heavily in prepositioned troops and supplies, on the other hand, amounts to the kind of static shoreline defense that has proven incapable of repelling invasions in the past.
Other analysts suggest that if Chinese forces are able to establish a beachhead, Taiwan should wage a guerrilla campaign that would make conquering Taiwan as painful as possible for China. Such proponents of asymmetric defense point out that Taiwan’s best hope for defeating a Chinese invasion would be to prolong the conflict and buy time for the United States to intervene on its behalf. The problem with such a strategy is that it is dependent on effective American intervention. Raymond Kuo states that “Asymmetric defense is ultimately predicated on the US military showing up,” and Michael Hunzeker admits that “Even asymmetry’s most ardent advocates accept that Taiwan’s military will struggle to hold out indefinitely without outside help.” Under America’s policy of strategic ambiguity, Taiwan cannot count on such intervention.
Given that reality, Taiwan cannot be expected to fully embrace asymmetric defense. Instead, the Taiwanese defense establishment will likely pursue a strategy that it perceives as giving them some chance of an independent victory, however slim. Given China’s overwhelming numerical and materiel advantages, it would eventually prevail in a conflict against Taiwan in which it establishes a secure beachhead. Since air and naval defenses cannot be guaranteed to prevent Chinese troops from making landfall on Taiwan, destroying Chinese beachheads will remain a Taiwanese imperative for as long as it faces the prospect of fighting a war alone. In light of the case studies above, this means Taiwan will likely attempt to maintain powerful mechanized forces as a backstop to its air, naval, and shoreline defenses.
This leaves the United States with two choices. First, it could abandon strategic ambiguity and attempt to persuade the Taiwanese to adopt asymmetric defense with the promise of American intervention. This would infuriate China, however, and have political repercussions that are beyond the scope of this article. Second, it could support Taiwan in establishing the defenses required to repel a Chinese landing, or else buy time for a potential American intervention. This would involve great financial cost and could aggrieve the Chinese as much as adopting a posture of strategic clarity. If neither option is taken, however, the United States could face the choice of launching a costly counteroffensive against a nuclear-armed rival to retake Taiwan—which is a much less credible policy option than providing for Taiwan’s defense in the first place—or leaving Taiwan to its fate under a conquering China.
The main point: Among other lessons, the recent history of amphibious operations suggests that mobile mechanized forces are an indispensable element of amphibious defense. However, Taiwan will struggle to establish the robust air, naval, and missile defenses necessary to defend these forces from interdiction on its own. The United States therefore has two basic options for improving Taiwan’s defense: it can either attempt to persuade Taiwan’s defense establishment to embrace asymmetric defense by adopting a policy of strategic clarity, or it can substantially increase financial and material support to Taiwan.
 Theodore L. Gatchel, At the Water’s Edge: Defending Against the Modern Amphibious Assault (Annapolis: Naval Institute Press, 1996)
 Gatchel, “Anti-Landing Defense: The Other Face of Amphibious Warfare,” in At the Water’s Edge.
 Gatchel, At the Water’s Edge, 47.
 Gatchel, “German Mobile Defense: Sicily and Salerno, 1943,” in At the Water’s Edge.
 Rick Atkinson, The Day of Battle: The War in Sicily and Italy, 1943-1944 (New York: Henry Holt & Company, 2007), 226-227.
 Ibid., 228-235.
 Ibid., 214.
 Ibid., 206.
 Gatchel, At the Water’s Edge, 55.
 Ibid., 128.
 Ibid., 137-140.
 Ibid., 140.
 Ibid., 143.
 Gatchel, “The Ultimate Naval Defense: Okinawa and Japan, 1945,” in At the Water’s Edge.
 Gatchel, At the Water’s Edge, 163.
 Atkinson, “Salerno,” in The Day of Battle, and Gatchel, At the Water’s Edge.
 Gatchel, At the Water’s Edge, 215-216.
 Ibid., 58.
 Ibid., 204-208.