On Sunday, Marines from the amphibious assault ship USS Tripoli fast-roped from helicopters onto the deck of the Iranian cargo ship M/V Touska to take custody of the vessel, the first seizure of the week-long U.S. military blockade of Iranian ports. The Touska was first disabled by sailors on the Navy destroyer USS Spruance, who fired several shots from its 5-inch MK 45 gun at the vessel’s engine room. Carried out under the cover of darkness, the operation highlighted the capabilities of a small, highly trained group of Marines known as a Maritime Raid Force, or MRF, that specializes in...