The United States is sending four minesweeping ships and four minesweeping helicopters to augment its naval forces in the Persian Gulf, the US Navy's top officer told a US Senate committee on Thursday."We are moving four more minesweepers to the region, making eight," Adm. Jonathan Greenert said in the Senate Armed Services Committee, declining to say when the deployment would take place.Later in January, US Joint Chiefs of Staff chairman General Martin Dempsey said that while Iran has the ability to block the Strait of Hormuz “for a period of time,” the US would take action to reopen it in such an event.“They’ve invested in capabilities that could, in fact, for a period of time block the Strait of Hormuz,” Dempsey said in an interview airing on the CBS “Face the Nation” program. “We’ve invested in capabilities to ensure that if that happens, we can defeat that.”Reuters contributed to this report.Iran has in recent months threatened to close the Strait of Hormuz in retaliation for sanctions levied against it by the United States and Europe. Approximately one fifth of the world's oil passes through the strait on a daily basis.In January, Greenert said that preparing for a potential conflict in the Strait of Hormuz is the kind of thing he loses sleep over."If you ask me what keeps me awake at night, it's the Strait of Hormuz and the business going on in the Arabian Gulf," said Admiral Jonathan Greenert, who became the chief of naval operations in September.