Chinese media reported on the seizure of a U.S. Navy underwater drone in the South China Sea. Beijing eventually returned the drone. (U.S. Navy/CCTV via Reuters)

Last week, China seized a U.S. Navy drone. The capture signaled Beijing’s displeasure with U.S. reconnaissance in the South China Sea, but avoided endangering U.S. personnel and giving Washington a reason to escalate.

Get used to this. Attacks on remotely controlled vehicles — drones — may become a new currency for coercive diplomacy, enabling nations to challenge rivals without hurting an opponent’s military personnel — and so without risking significant escalation.

So far, states appear to react differently to drones than to manned assets, even though the two are equivalent under international law. Both unmanned and manned military vehicles can freely navigate and fly over international waters and through international airspace. At the same time, states maintain the right of self-defense against any vessel or aircraft — manned or unmanned — that penetrates national airspace without authorization or poses a threat when operating in a state’s territorial waters.

This has happened before.

China isn’t the first nation to violate international law by seizing a U.S. military asset in international territory. Iran did something similar when it attempted to shoot down a U.S. Air Force Predator drone over the Persian Gulf in 2012.

To be sure, the Chinese and Iranian militaries have also responded forcefully to manned U.S. military aircraft and ships in international waters, but generally by harassing them, not seizing or destroying. Beijing did, however, detain the crew of a U.S. reconnaissance plane in 2001 after the aircraft landed in China following a midair collision with a Chinese fighter jet.

Other nations have also targeted U.S. drones operating in their national airspace, while avoiding attacking manned U.S. aircraft. For instance, Syria downed a U.S. Air Force Predator in early 2015. Iran claimed to hack the controls of a stealth RQ-170 drone, capturing it in 2011. In contrast, no public reports suggest that either country tried to deliberately capture or destroy manned U.S. planes.

This potential isn’t entirely new. Archival materials reveal that U.S. officials were concerned about precisely this throughout the Cold War. One senior State Department official during the Johnson administration, for instance, feared that operating reconnaissance drones over Cuba instead of manned U-2 spy planes would “invite a shoot-down.

In their seminal work on international crises, political scientists Glenn Snyder and Paul Diesing suggest that low-scale military actions that do not threaten a target’s core interests may be enough to influence a state’s behavior — to send a message — without sending a crisis out of control.

That may be what’s happening now. Washington has generally avoided retaliating when its drones are attacked, choosing not to escalate. The Obama administration’s response to last week’s drone seizure was described as “muted,” and Syria’s 2015 attack on a Predator got little media attention.

Lack of escalation makes sense for these three reasons.

First, leaders deploy drones in large part to prevent casualties and drawn-out conflicts. If a state doesn’t want to get into a war, losing a machine — but not a person — is unlikely to change its mind. 

Second, the public probably wouldn’t support going to war over a lost machine. As part of an ongoing project, I surveyed 1,210 Americans about their perceptions of drone operations. Unsurprisingly, I found that Americans are less likely to call for hawkish retaliatory measures if a U.S. Air Force reconnaissance drone is shot down than if the same happens to a spy plane with a pilot aboard.

Third, for many of the same reasons, Americans and observers internationally may see retaliation over the loss of a drone as excessive, a disproportionate use of force.

There’s a big difference between seizing a machine — and seizing a machine with a person in it

To be sure, states are unlikely to respond directly with force even after the loss of manned assets. But tensions can be more easily defused and crises more quickly de-escalated when lives are not at stake.

For instance, China returned the U.S. Navy drone less than a week after it was seized following negotiations between Beijing and Washington. In contrast, the crew of the American EP-3 reconnaissance plane that landed in China in 2001 was detained for nearly two weeks before being released amid a series of widely publicized and highly charged statements by leaders on both sides.

In short, there’s a big difference between a military machine and a military machine with a living person on it. Drones are increasingly viewed as an attractive and low-risk means of replacing manned ships and planes on dull, dirty and dangerous missions.

China’s recent drone seizure, however, may prompt policymakers and military commanders to consider more carefully whether rivals will be more likely to attack drones.

Erik Lin-Greenberg is a PhD candidate in the department of political science at Columbia University. His research examines the effects of technology on armed conflict.

This post has been corrected to note that Iran captured the stealth RQ-170 drone in 2011.