India, June 18 -- The US last week struck three commercial tankers in the waters off Oman, killing three Indian sailors and triggering operations to rescue dozens from the burning and sinking vessels. The action, the US said, was to enforce its naval blockade for vessels coming from or going to Iran.

The strikes drew a formal protest from New Delhi, but the US asserted that the three ships had violated its blockade imposed since mid-April. The ships' crews, and in at least one case, the management company, denied the charges.

But the episode brought a separate question into focus: the flags on the masts of those vessels.

Two flew the flag of Palau, a small island nation in the western Pacific Ocean, and the third flew the flag of Guine...