A week ago, a small tanker ship approached the Persian Gulf after a 19-day voyage from China. The captain, as required by international rules, reported the ship’s position, course, speed and another key detail: It was riding high in the water, meaning it was probably empty.

Then the Chinese-owned ship, the Sino Energy 1, went silent and essentially vanished from the grid.

It reported in again on Sunday, near the spot where it had vanished six days earlier, only now it was heading east, away from the Strait of Hormuz near Iran. If past patterns hold, the captain will soon report that it is riding low in the water, meaning its tanks are most likely full.

As the Trump administration’s sanctions on Iranian oil and petrochemical products have taken hold, some of the world’s shipping fleets have defied the restrictions by “going dark” when they pick up cargo in Iranian ports, according to commercial analysts who track shipping data and intelligence from authorities in Israel, a country that backs the Trump crackdown.

[Iran breached a nuclear fuel limit in what it said was a response to the reimposition of sanctions by the Trump administration.]