The “dark fleet” of ships hauling Russian cargoes may be spreading. The Wall Street Journal reports that a Russian merchant ship whose owner has allegedly carried weapons for the Kremlin turned off its transponder last month before surreptitiously docking at South Africa’s largest naval base.

The ship, named Lady R, owned by Russian shipping company MG-FLOT, delivered and loaded unidentified shipments.

The visit has strained relations between Washington and Pretoria. It also demonstrates the difficulty for the U.S. and its allies of enforcing sanctions against Moscow. 

The Lady R took conventional tactics such as turning off transponders that ships have been using to evade tracking. According to witnesses and photos, a mobile crane moved crates off and onto the 122-meter-long vessel under the watch of armed guards for two nights, even as Simon’s Town, where the base is located, was plunged into darkness by nationwide power cuts.