A training exercise went disastrously wrong Sunday in the Gulf of Oman when an Iranian missile struck one of its own fleet, killing at least 19 sailors and injuring a further 15. The Associated Press reports the missile accidentally struck a support vessel near an intended practice target. It’s believed that the vessel was arranging targets for other ships to shoot, but it remained too close to one explosion. The friendly fire incident took place near the port of Jask, around 800 miles southeast of Iran’s capital city of Tehran. It’s the second serious incident involving a misfired missile by Iran’s armed forces this year. In January, after attacking U.S. forces in Iraq with ballistic missiles, Iran’s paramilitary Revolutionary Guard mistakenly shot down a Ukrainian jetliner, killing all 176 people on board.