Franklin D. Roosevelt was almost killed by a US warship 

In November 1943, the battleship USS Iowa and three destroyers including the USS William D. Porter (or Willie Dee as it was called)were on a top secret mission in the Atlantic Ocean. The Iowa's precious cargo being US president Franklin D. Roosevelt, high ranking US military officers and the Secretary of State; Cordell Hull. During the journey, all ships were to maintain radio silence as to avoid the threat of German U-boats. On 14 November, president FDR wanted to test the Iowa's defenses in an event of an air attack, the Iowa launched weather balloons to simulate targets for the anti-aircraft gunners. The Willie Dee was preparing for a live torpedo drill- where primers or small explosive charges are removed for practice. But, a torpedoman had forgotten to remove the primer from a torpedo before it was to be "fired" at the Iowa. The torpedo was fired and as soon as the crew realized it was a live torpedo, they tried contacting the Iowa via signal lights, but nothing worked. The crew of the William D. Porter decided it was necessary to break radio silence to tell the Iowa of the threat, when Roosevelt heard of the incoming torpedo he asked to be moved to the railing so he could see it. Fearing an assassination plot on the president, the guns of the Iowa were aimed at the destroyer, but fortunately, the torpedo hit the heavy waves produced by the Iowa's speed. The whole crew of the William D. Porter were arrested and sent to Bermuda to face trial. A torpedoman, Lawton Dawson confessed to the incident and was sentenced to 14 years of hard labor, but Roosevelt intervened, asking that no punishments be levied at the crew after the accidents.