Tehran reports that an Iranian naval patrol Thursday, May 27, detected a USnuclear submarine sailing through the strategic Strait of Hormuz, through which most of the oil produced by Persian Gulf states passes on its way to world markets. DEBKAfile's Iranian sources report Tehran has placed its navy and army on high alert.
Western intelligence and naval sources confirm that a nuclear-armed American submarine has in fact entered the Persian Gulf. This confirms DEBKAfile's report of May 20 that the Obama administration had decided to boost USmilitary strength in the Mediterranean and Persian Gulf regions in the short term with an extra air and naval strike forces and 6,000 Marine and sea combatants. Carrier Strike Group 10, headed by the USS Harry S. Truman aircraft carrier, was due to sail out of the US Navy base at Norfolk, Virginia Friday, May 21.
On arrival, it was to raise the number of US carriers off Iranian shores to two. 
Thursday's arrival of a US nuclear submarine also ties in with the currently rising military tensions alongIsrael's borders with Syria and Lebanon.
Up until now, President Barack Obama kept just one aircraft carrier stationed off the coast of Iran, the USS Dwight D. Eisenhower in the Arabian Sea, in pursuit of his policy of diplomatic engagement with Tehran.