An unnamed US ballistic-missile submarine arrived in Gibraltar on Monday amid persistent tensions with Iran. US Navy courtesy photo The Pentagon shared a photo of an Ohio-class ballistic-missile submarine docked in Gibraltar. The Navy said the submarine's visit demonstrates US capability and commitment to NATO allies. Sharing the location of a nuclear-armed submarine sends a clear message to adversaries. The US military rarely discloses the locations of its deployed ballistic missile submarines , the naval arm of its nuclear might. When it does, it's often meant to send a message.…