The US Navy staged its latest show of military force off the Iranian coastline on Wednesday, sending two aircraft carriers and landing ships packed with 17,000 US Marines and sailors to carry out unannounced exercises in the Persian Gulf. The carrier strike groups led by the USS John C. Stennis and USS Nimitz were joined by the amphibious assault ship USS Bonhomme Richard and its own strike group, which includes landing ships carrying members of the 13th Marine Expeditionary Unit. The Navy said nine US warships passed through the narrow Strait of Hormuz on Wednesday. Merchant ships passing through the busy strait carry two-fifths of the world's oil exports. Aircraft aboard the three carriers and the Bonhomme Richard were to conduct air training while the ships ran submarine, mine and other exercises. The maneuvers came just two months after a previous exercise in March when two US carrier groups carried out two days of air and sea maneuvers off the Iranian coast. Before the arrival of the Bonhomme Richard strike group, the Navy maintained around 20,000 US personnel at sea in the Gulf and neighboring waters. US warships have frequently collided with merchant ships in the busy shipping lanes of the Gulf.