US President Donald Trump said on Tuesday that Iran was responsible for downing an American military helicopter near the Strait of Hormuz and that the US “must” respond to the attack.Trump made the comment in a social media post after a drone boat rescued the crew of the Apache attack helicopter that crashed near the strategic waterway, which Iran has effectively closed during its war with the US and Israel.It was the first known drone rescue at sea by the US military, said Capt Tim Hawkins, a spokesman for US Central Command. He said the unmanned boat located the two aviators and brought them to shore after they spent about two hours in the water.