In recent weeks, Syrian opposition groups have renewed calls for the United States and other countries to supply man-portable air defense systems (MANPADS) to Syria’s beleaguered rebel forces. Senator John McCain has proven a lone voice in advocating for the provision of MANPADS to American–trained rebel forces in what he openly describes as a prospective replay of Washington’s covert war against the Soviets in Afghanistan. Russian media have highlighted some of the many dissenting expert opinions.

Other states may not be quite as cautious, however. Qatar is believed to have delivered Chinese FN-6 MANPADS to Syrian rebel groups. Several of these have since been acquired by the Islamic State. Saudi Arabia, which has increased arms shipments to the Free Syrian Army in response to the Russian intervention, reportedly “hasn’t ruled out” supplying these advanced surface-to-air systems.

It remains very unlikely that the U.S., at least, will supply Syrian rebel forces with MANPADS—the potential for accidental or intentional misuse, and the potential for these systems to be used against Russian aircraft now operating in Syria, is simply too great. If MANPADS were supplied to Syrian rebel forces, the concerns regarding further proliferation and misuse are very real. Guided light weapons have already proliferated within Syria, with TOW 2A missile supplied to moderate groups having been captured and employed by extremist forces such as Jabhat al Nusra and the Islamic State. If such weapons were to be supplied, however, there are possible safeguards which could be put in place to track and control the custody of these missile systems.

First, there are buyback and destruction programmes, which have served as long-standing U.S. policy tools in regions where MANPADS have proliferated. While these programmes have experienced some success—the U.S. State Department reported having destroyed more than 30,000 MANPADS by July 2009—they are expensive to operate, and tend not to deter the more extremist elements in possession of guided light weapons. At least 50 non-state armed groups are believed to possess MANPADS, and these weapons have been documented outside of state control during and after recent conflicts including those in Libya, Syria, Mali, South Sudan, and Ukraine.

Several other methods for controlling the weapons themselves have been proposed, although remain mostly theoretical. The earliest concepts centered on a desire to disable guided weapons remotely; essentially to install a remote “kill switch.” This was later refined to a “controllable enabling” model, which goes a step further by ensuring that a weapon cannot be armed until outside authority is given. Collectively, these measures are referred to as “technical-use controls.”

Several technical-use controls have been suggested, with some of the major concepts including:

• Timer-based disabling (disable a weapon after a set time period has elapsed, either irrespective of outside input, or unless returned to an authorised location or user);

• Remote kill switches (remotely disable a weapon, permanently, semi-permanently, or temporarily);

• Geographic lock-out systems (automatically disable a weapon if it leaves certain geographic bounds, determined by GPS or otherwise);

• Coded enabling (a code, external device, authorised fingerprint or similar is required to arm the weapon);

• Remote enabling (a form of controllable enabling);

• Permissive action links (a form of controllable enabling);

• Selective target enabling (restrict target profiles to those with/without certain signatures; i.e., enable a weapon to target small aircraft but not larger ones, such as civilian airliners);

• Several other measures and combinations of the above.

In terms of flexibility, the concept of controllable enabling offers the most to governments seeking to influence when, where, and how guided light weapons are employed by parties they have supplied. MANPADS fitted with a controllable enabling device would require outside authorization before the munition could be armed and fired. A more advanced version of the controllable enabling concept is the permissive action link (PAL), an idea borrowed from nuclear weapons. This is a two-way system which requires the operator to input a “request code” and a higher authority to remotely transmit the data allowing the weapon to operate with a “response code.” The effects could vary, but suggested models have included enabling the weapon for a set period of time. A PAL would be relatively complex, and so could also include other forms of technical-use controls, such as biometric requirements or remote kill switches.

At its most basic, a controllable enabling measure could require the weapon operator to radio a higher authority (such as a liaison officer from the country supplying the system) and request that the weapon be, in essence, “turned on.” The liaison officer would likely use other data in her assessment of whether or not to enable the weapon. Perhaps she has GPS data indicating the unit’s position, and can confirm they are in a contested area, or perhaps there is electronic intelligence indicating the clear presence of an aerial threat near the unit’s position. Of course, these procedures would impact the end user’s ability to employ such a weapon quickly, which could have significant tactical implications. There is also the ever-increasing risk of operating within an environment where communications signals such as GPS are spoofed or denied (jammed).

There are other likely drawbacks as well, including significant costs and complication of the logistics chain. Implementation of these methods of control would also require, in most cases, the cooperation of the manufacturers of guided weapons. Modifications could be made to the launch assembly or the missiles themselves, depending on the desired outcome and other parameters, such as the size and nature of modifications. In some cases, modifying existing and legacy weapon systems would not be feasible, or would be prohibitively expensive. More complicated technical-use controls would require significant staffing support and field equipment. Finally, any such systems are likely to require a significant amount of “real world” testing, and risk alienating those who are supplied with guided light weapons featuring faulty or ill-conceived technical-use controls.

None of these technical-use controls are likely to prove a panacea to the threat of guided light weapons proliferation. There are already tens of thousands of such systems in the illicit sphere. Some may also wonder whether the introduction of technical-use controls could have unexpected effects, such as lowering the export threshold for MANPADS—a process that is heavily regulated in many states.

Initially, at least, weapons featuring technical-use controls will likely only be suitable for transfer to smaller states or non-state armed groups. There have been persistent rumours of U.S. weapons systems in recent conflict zones fitted with technical-use controls, but no hard evidence has emerged to date.

If the U.S. and NATO states were to pursue such measures, are other major suppliers of guided light weapons—such as Russia and China—likely to follow suit? Polish company MESKO S.A., manufacturers of the Grom (‘Thunder’) series of MANPADS, will produce a new model incorporating “anti-proliferation measures”, according to the Polska Grupa Zbrojeniowa (Polish Armaments Group). It is not clear what these measures will consist of, but they may include technical-use controls. These will supposedly enter production by early 2016.

For all of the clamouring from Syrian opposition forces, the U.S. and other Western states are very unlikely to introduce more MANPADS into the conflict zone. As such, most of these technical-use controls will likely remain theoretical for a while longer. Other states which might supply MANPADS to rebel forces are unlikely to implement such controls, leaving open the possibility of further unexpected proliferation of these weapons. To a rebel group, MANPADS represent a highly mobile, compact weapon system capable of engaging many of the Syrian military’s aircraft. To a terrorist organisation, however, MANPADS may have value as a concealable, portable threat to both military and civilian aviation targets.