The idea that the Iranians could approach a US warship and tag it while underway is ridiculous. Even if the Iranians used some sort of mega-spraypaint technology, their sub would be detected...by sonar, not radar. Imagine how hard it would be for a mini-sub to maintain station next to a moving ship and "etch" anything into its hull. If there is a grain of truth to the story, then the Iranians had to have approached a ship in port...most likely something like a tug, or a transport ship sitting at a dock in Dubai. The whole idea is silly...even if it were true it would mean that the Iranians have stupidly alerted the US Navy to one of their new capabilities. Ridiculous.
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from the article: Iran Revolutionary Guards: Unit engraved emblem on U.S. ship