ADEN, June 10 -- The ship's armed security team was already on watch. At 4:30 in the morning, a small craft appeared out of the darkness carrying six men with guns, closing fast on the cargo vessel from the south-west. What followed was a brief, sharp exchange of fire - and then the attackers turned away.

The UK Maritime Trade Operations (UKMTO), the Royal Navy-run maritime security coordination centre in the Gulf, logged the incident at approximately 88 nautical miles southwest of Balhaf, a port on Yemen's southern Shabwa coast, and issued Warning 065-26 to vessels transiting the area. No casualties or damage were reported. Authorities said they were investigating.

That investigators have not named a perpetrator is, on its own, the mos...