Last week, World Peace Foundation staff hopped on the ferry to Georges Island, one of the numerous small outcroppings in Boston’s harbor, to celebrate the end of the academic year. Georges is home to Fort Warren, an old U.S. military installation built in the early nineteenth century and retired after WWII. It served as a defensive position athwart the only navigable path for large ships through the hidden shallows of the harbor. Bristling with artillery emplaced behind earthwork and concrete, the fort challenged ocean-goers for a century before it was demilitarized and handed over to the state of Massachusetts.
Fort Warren and similar armed fortifications raise an important conceptual problem for peace studies and advocacy: is there such a thing as a purely ‘defensive’ weapon, and is the promotion of ‘defensive’ strategies and force postures a viable incremental path toward peace? The right answer is “sometimes,” and only when taking other factors into account. However, the concept of a purely ‘defensive’ weapon has proven ripe for abuse.
The belief that building purely defensive militaries can pave the way toward permanent peace enjoyed its first moment in the limelight during the interwar disarmament conferences at Geneva. Negotiators made an effort, with varying degrees of sincerity, to classify weapons as favoring offense or defense, restricting the former while encouraging the latter. These talks never bore fruit for the same reasons that all other mechanisms in the League of Nations system failed: absent the willingness of the system’s defenders to drive the agenda, bad-faith revanchists and imperialists subverted processes to their own ends.
At sea, arms reductions negotiations did succeed, but again only for a time. The 1922 Five Power Treaty signed between France, Italy, Japan, the United Kingdom, and the United States is well known for setting a capital ship ratio between the parties, with which Japan later became dissatisfied. Less well remembered is that the treaty also prohibited the construction of new fortifications in the Pacific, thereby limiting outside powers’ force projection to the benefit of Japan. These talks suggest that states know well that even the most purely defensive military investments—armed forts—can have offensive implications.
A more (temporarily) successful application of the defensive approach to peace on land is evident in the 1990 Treaty on Conventional Armed Forces in Europe and the long negotiations through the 1970s and 1980s which made it possible. From the start, NATO negotiators aimed specifically to limit weapons capable of seizing and holding territory—namely tanks, armored combat vehicles, and artillery. The Soviet proposal of mid-1988 suggested the complete restructuring of forces, after initial reductions, into purely defensive orientations. Thus, both sides worked from the implicit assumption that armies can be configured to be more defensive and thus more peace-prone.
At the same time that these talks progressed—from impasse in the 1970s, to speculative counter-proposals in the 1980s, and a rush to the finish in 1988-1990—political scientists were debating how the offense-defense distinction could fit into models for explaining patterns of war and peace. While policy-makers were focused on offensive and defensive types of weapons, scholars were more interested in periods of offense- and defense-dominance in warfare in aggregate. Robert Jervis wove the idea of offensive- and defensive-superiority into his seminal 1978 explanation of the security dilemma. In response, Jack Levy questioned whether any periods of military history could be sorted so neatly into offensive or defensive superiority based on military technology. He nonetheless agreed that certain weapons types—those affording more tactical mobility and potential for movement—could be classified as more beneficial to the offensive. Over the last few decades, theorists have moved from quibbling over conceptualization and measurement to a focus on offensive and defensive doctrines in addition to technologies.
Clearly, the concept of the defensive weapon has some purchase among both policy-makers and military strategists. While analysts can disagree in their assessments of a specific weapon systems’ ‘defensiveness,’ there is usually a degree of consensus about the tactical-level effects of easy cases such as tanks or armored vehicles. There are three types of problems, however, that muddy this otherwise coherent concept. First, the tactical effects of defensive weapons cannot be assessed outside of the context of a military’s overall force composition and doctrine. Taiwan is in talks with the United States to purchase 108 M1A2 Abrams main battle tanks; in the context of its strategic position, it is likely that these would serve a purely defensive purpose against the threat of a Chinese amphibious landing. While offensive weapons such as tanks can be defensive in context, defensive weapons can also contribute to offense at the tactical level. For example, a mobile surface-to-air missile system can protect an armored advance from defensive air power.
Second, while some military systems can be defensive at the tactical level, they can be offense-enabling at the strategic level. The example given above of US and UK naval fortifications in East Asia is an old one. A newer one is the well-known problem of defense against nuclear attack: a perfect nuclear shield would break mutually assured destruction and encourage use of nuclear weapons with impunity. The historical exhibit at Fort Warren includes a Nike Ajax surface-to-air missile; these, as well as their nuclear-tipped Nike Hercules successors, were deployed in the early Cold War to protect Boston against Soviet bombers. Today, that legacy lives on in the US military’s many missile-defense programs, but most directly in the Ground-Based Interceptor, a small, ostensibly rogue-state-focused missile defense system that keeps alive the dream of a national nuclear shield.
The third problem is more subtle and speculative: the allure of defensive weapons can have negative effects on a country’s grand strategy, and therefore its appetite for war. The dream of a perfect ballistic missile shield, immunizing the homeland from nuclear blackmail, would grant the United States the freedom to separate its active foreign policy overseas from the consequences of that policy at home. Similarly, the pursuit of the forever war against global terrorism, waged officially as a preemptive defensive response to the threat of terrorism (and accepting this as ‘defensive’ for the sake of argument), severs the thermostatic link between US foreign policy and feedback from the ‘others’ on which it acts. Objects of US policy have few modes of recourse: they can remonstrate, retaliate violently, or realign. The first option has obvious limits. By successfully numbing itself to small acts of violence, the US places itself at two risks: of artificially diminishing public perceptions of the risks of conflict leading to overreaction when the ‘bomber’ ultimately gets through, and of diplomatic realignments that promise future damage to US interests. Of course, preventing terrorist attacks is a perfectly legitimate state responsibility. But without a concomitant improvement in US receptivity to foreign signals, policy becomes leprous, numb to consequences. Consequences cannot be deferred forever, but as long as they are, excellence in defensive arms will tend to encourage over-commitment and adventurism.
This is only one way that the concept of defensive weapons can lead to abuse. Others are more quotidian: the arms industry is, of course, better known in policy discourse as the “defense industry,” and arms exports are justified in terms of their contributions to maintaining the defensive side of a balance of power. For these reasons, caution is always warranted when advocates sing the praises of defensive weapons. Yes, some weapons are more conducive for defense and perhaps the idea of a defensive army can contribute to peace settlements and negotiated arms reductions. But one must understand the context and be wary of abuse.
Returning to Fort Warren, it is hard to argue that the installation had any effect on the military balance of power after it became obsolete—as the historical exhibit mentions—around the turn of the century. It was not only the fast and numerous revolutions in naval technology of the pre-WWI era that rendered the fort obsolete, the strategic context—specifically US vulnerability to British coastal raiding—had also changed irrevocably. The appropriate lesson to be learned from Fort Warren, then, might be that military investments can be hard to unwind, even after they are no longer useful. But land-based naval defenses are enjoying a comeback. The US Army is investing in a new generation of missiles that will help it control coastal waters, with the Pacific theater clearly in mind. Whether these will improve prospects for peace in the region or not is a difficult question, and hinges as much on intentions, perceptions, and broader strategic dynamics as any qualities of the weapons themselves.
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