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Senior Fellow, Carnegie Endowment for International Peace
April 15, 2019
Proliferation Security Initiative: Ten Years On

Arms Control NOW

In Warsaw, the WMD interdiction initiative is getting a second look, and hopefully a second wind.

By Ian Williams

 Singapore Customs Authority) (Image Source: Singapore Customs Authority)

May 31st marks the 10th anniversary of the Proliferation Security Initiative (PSI), a non-binding international effort to stop the trafficking of weapons of mass destruction and related materials. Member states are currently holding their first PSI High Level Political meeting in five years.

The May 27-29 meeting is a critical opportunity for the Obama administration to take action on its pledge from the 2010 National Security Strategy to turn the initiative into a "durable international effort." It will also give the administration a chance to answer critics who have accused it of allowing the WMD interdiction initiative to wither and atrophy.

An Evolving Initiative

The Proliferation Security Initiative was formed in May 2003 in response to the failed interdiction of the So San, a North Korean freighter carrying ballistic missiles to Yemen. U.S. and Spanish naval forces cooperated to interdict the vessel, but the Yemeni government insisted the missile shipment was the product of a legitimate transaction in accordance with international law.

The episode, along with concerns about the illicit trade in nuclear weapons technology, prompted the George W. Bush administration to launch the Proliferation Security Initiative. The initiative's purpose is to increase participating states' capacity to interdict consignments of WMD related materials while in transit. Often described as "an activity, not an organization," PSI carries the hallmark of having no permanent institutional structure. There is no headquarters, no secretariat, and no standing committees.

Membership in the PSI only requires a state to endorse a shared Statement of Interdiction Principals (SIP), which provides the framework for cooperative action on interdictions. This low bar for entry has allowed the PSI to expand rapidly. To date, 102 states have endorsed the SIP.

Participating states share intelligence, best practices, and participate in training exercises, such as Deep Sabre, a multinational maritime interdiction exercise conducted in the South China Sea in 2005. These activities are organized on an ad hoc basis by the PSI Operational Experts Group (OEG). The OEG is comprised of 21 states, which meet the somewhat subjective criteria of being the "most active and strongly engaged" members. The OEG convenes on a periodic basis to plan future activities, discuss recent interdiction operations and other relevant matters.

PSI proponents argue that the initiative's non-institutional nature is in fact its greatest strength. Without a codified structure, the focus of PSI rests on action, rather than procedure. This model of non-institutional multilateralism is very much a reflection of the frustrations felt by the initiative's architects towards international institutions and accompanying bureaucracy.

However, because of its lack of self-sustaining institutions, the PSI requires active stewardship and consistent participation from member states. Without such constant care and attention, the PSI is vulnerable to gradual deterioration.


Recently, the Obama administration has been criticized by some Republican congressmen for allowing the PSI to "languish," and encouraged increasing interdiction efforts. There is some evidence to suggest PSI activity has declined since 2009, at least quantitatively.

According to State Department records, the number of OEG meetings that occurred during the Bush administration numbered between 3-5 per year. Since 2009, that number has declined to 1-2 per year. The number of PSI-related training exercises and activities has also declined by around half.

The administration has countered these critiques, by pointing out that there have been numerous interdictions of WMD consignments in transit under its watch. David Asher, Center for a New American Security senior fellow and former George W. Bush administration official, noted in a recent interview that more interdictions have occurred during President Obama's time in office than during the early years of PSI during the Bush Administration.

However, it is very difficult to confirm any details about PSI operations through open sources, since so very few interdictions are ever made public. Moreover, the overall lack of transparency makes it difficult for open source analysts and think tanks to assess the overall success of the initiative. It also makes it hard to evaluate how the initiative could be improved. Even the discussions that take place at OEG meetings are generally kept secret and only brief concluding statements are released.

A Way Forward

Nevertheless, Aaron Dunne at the Stockholm International Peace Research Institute (SIPRI) has been able to slice through the initiative's opaqueness and produce an insightful report on the current challenges facing the PSI and give some sound recommendations on ways to improve its efficacy.

Released in May, the report says that most PSI interdictions occur while vessels suspected of transporting WMD related materials are in port, rather than on the high seas in international waters. This is in contrast to the popular perception that most PSI operations involve commandos in black masks storming freighters filled with centrifuges. As much as that captures the imagination, it does not reflect the "operational reality" of PSI, at least not most of the time.

However, Dunne also finds that much of the PSI activities such as training exercises, as well as the composition of OEG delegations, are still militarily oriented. Reorganizing OEG delegations to be more representative of national customs authorities, and including more customs personnel in training exercises are two ways the PSI could be improved, Dunne argues.

The SIPRI report also suggests that strengthening the legal underpinnings for interdictions would enhance PSI. The PSI does not create new law – national or international. It merely acts as a mechanism to enforce existing law.

Currently, much of the legal basis for PSI actions stems from UN Security Council Resolution 1540, UN Convention on the Law of the Sea, and the Convention on the Suppression of Unlawful Acts. Dunne recommends that all OEG members must sign, ratify and implement these treaties and resolutions, or be expelled from the OEG.

Furthermore, Dunne recommends that a set of minimum national laws and practices should be more clearly defined for member states. As most interdictions take place within national territories, the development of national legal regimes criminalizing the transport of WMD related materials is critical for PSI enhancement. After all, the interdiction of the So San did not fail because of a failure of intelligence sharing or military cooperation, but rather because of a lack of legal authority to seize the missiles.

The Time is Now

These reforms, which are in no way exhaustive of the full range of recommendations laid out in SIPRI's report, are just some examples of the kinds of steps that can be taken to enhance and reinvigorate PSI. The 10th anniversary meeting currently taking place in Warsaw is an opportunity to update the initiative on the basis of the lessons learned over the past ten years, and to make sure it remains a useful tool in the battle against proliferation for years to come.