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The US military has been secretly guiding some commercial ships through the Strait of Hormuz in an effort to move stranded vessels out of the region.

Getting into it: According to US officials cited by The New York Times and The Wall Street Journal, CENTCOM has guided around 70 commercial ships through the strait over the past three weeks, which works out to roughly three a day. The catch is that most of these ships are sailing “dark,” switching off their Automatic Identification Systems (the beacons that normally broadcast a vessel’s position to prevent collisions) to make themselves harder for Iran to detect and target. Cut off from those electronic signals, the ships instead rely on the US military, which uses radar, drones, and other shit to track their movements, and coaches captains on when to switch the systems off and how to handle whatever Iran throws at them.

US officials have been careful about how they describe the effort. “Though U.S. forces are not escorting, we continue to communicate and coordinate with commercial ships seeking to freely and safely transit the Strait of Hormuz,” Central Command spokesman Capt. Tim Hawkins said. Officials admit they’ve kept the whole thing low-profile so Iran doesn’t start hunting the ships that use it.

It’s a more cautious approach than “Project Freedom,” the operation Trump announced in early May to escort stranded ships, which he scrapped within days, partly because the Saudis wouldn’t give US forces access to their airspace or a key air base. Even during that operation, a French container ship coordinating with the military was attacked, and Central Command said the ship had ignored some of its rules.

The arrangement has become a rare bit of breathing room for the global economy, but an enormous risk for shipowners, especially as war-risk insurance premiums are as much as 4% of a ship’s value, up from a quarter of a percent in peacetime.

This all comes as Iran, which insists it controls the waterway, has carved out its own toll route and attacked ships that cross without permission. It has also set up a Persian Gulf Strait Authority that the US has sanctioned and declared off-limits.