What we know about US sea drone used in helicopter crew rescue mission

A sea drone was used to save two crew members of a downed US army helicopter off the coast of Oman earlier this week, according to the US military - making it the first publicly known instance of an unmanned vessel being used to conduct a rescue mission. President Donald Trump said the apache helicopter was shot down by Iran near the Strait of Hormuz - the dangerous waterway which has been largely blocked off to shipping since the start of the Iran war. The two soldiers were safely rescued within approximately two hours and are in stable condition, US Central Command (Centcom) said. BBC Verify has examined what we know about the drone boat and how the mission took place. What is the US sea drone?