Iran grabbed two of the Navy’s Saildrones earlier this month. Why?

In response to the second of two incidents, the Navy pointed out that the uncrewed vessels were "taking unclassified photos."
A Saildrone in the Red Sea in April, with the USS Mount Whitney in the background. US Army / DeAndre Dawkins

For 20 hours, from 2 pm local time on September 1 to 8 am the next day, Iran’s Navy seized and held two robot scouts used by the US Navy, before their return was negotiated. The action took place in the Red Sea, where the US has operated the Saildrones since December 2021. The incident followed the attempted capture of a Saildrone in the Persian Gulf by Iran on August 29, when a Saildrone was towed by the Iranian Navy before being released as US ships arrived. The incidents, which passed without bloodshed, are a curious feature of modern not-quite-warfare, demonstrating the vulnerabilities and benefits of robotic craft at sea.

What is a Saildrone?

The Saildrones are, as ocean-faring craft go, quite small: 23 feet long, 15 feet tall above the surface, and just 6 feet deep underneath it. To help other ships steer clear, Saildrones broadcast their location (and receive the location of other ships) from Automatic Identification System transceivers. Saildrones are also monitored remotely, allowing distant human operators to keep track of, and redirect, the drones as needed.

[Related: The feats of engineering that dazzled us in 2021]

The Red Sea is a long body of water, stretching over 1,200 miles from the Bab al-Mandab Strait to the mouths of the Gulf of Aqaba and the Gulf of Suez. Since at least December 2021, the US Navy has operated Saildrones in the Gulf of Aqaba. The uncrewed vessels have tremendous range, thanks to their use of batteries and solar power to maintain electronics and wind to provide propulsion. NOAA, which also uses Saildrones for weather monitoring and research, lists the range of the Saildrones in its use as over 16,000 nautical miles (18,400 statute miles), and Saildrone itself, the company that makes the similarly named robots, says the range is unlimited.

Seaways, like the Red Sea and the Strait, are governed by the UN Convention of the Law of the Sea, a set of shared rules agreed to by nations allowing safe transit through international waterways. The US is not a signatory to the convention but by policy follows all its rules regarding waterway navigation

Why might Iran seize them?

In its statement on the August 29 towing of a Saildrone, the US Navy said: “The Saildrone Explorer USV the IRGCN [Islamic Revolutionary Guard Corps Navy] attempted to confiscate is U.S. government property and equipped with sensors, radars and cameras for navigation and data collection. This technology is available commercially and does not store sensitive or classified information.”

By highlighting the commercial nature of the technology used, the US Navy is dialing down the inferred harm from the recent incidents, as well as minimizing potential for greater harm should a Saildrone be seized and studied for a longer time. If the Saildrone only uses cameras, radar, and navigation tools on the open market, then conceivably, Iran could just obtain those same technologies through open-market purchases. (Some weapons, like missiles and military-specification drones, are governed by strict export controls, their very make and operation inherently restricted from such sales.)

“The unmanned surface vessels were unarmed and taking unclassified photos of the surrounding environment while loitering in an assigned patrol area at least four nautical miles from the nearest maritime traffic lane. The vessels posed no risk to naval traffic and had been operating in the general vicinity of the Southern Red Sea for more than 200 consecutive days without incident,” the US Navy declared in a statement on the September incident.

Like the statement from the temporary seizure in the Red Sea, both emphasize that Saildrones are not vessels that create or contain secrets. They are, primarily, robots that take pictures of what’s around them. Keeping sensitive technology out of the hands of enemies at war or rivals in peace is a fundamental military mission; it’s what made Ukraine’s capture of an undestroyed Russian electronic warfare truck headline-grabbing news.

What could be gleaned by Iran, beyond the commercial tech and the unclassified photos, is a sense of what exactly the US Navy tasked the Saildrones with photographing. That would require gaining access to the drone’s data storage during the capture, or more likely (as with the incident in the Persian Gulf) towing the drone to a port where it could be studied and accessed. In the US Navy description of events, once the Saildrones were discovered seized, US ships pursued and flew helicopters as a part of encouraging a negotiated return of the drones.

The stakes, for now, are largely about shared use of the seas, between two navies without a tremendous amount of trust in one another. Because the Saildrones are uncrewed, when they are captured, no lives are at stake. There’s no person in peril. While the machines could be destroyed, that’s a loss of material, not casualties of war.