In the early hours of Tuesday morning, a cargo ship leaving the US city of Baltimore catastrophically struck a major bridge. The entire middle section of the 1.6-mile-long Francis Scott Key Bridge collapsed into the Patapsco River.  The ship lost power as it left the port, but the crew had enough time to make a mayday call so officials on the bridge were able to shut it to most traffic. Two people were rescued from the water but several people are still missing.  There are now questions about how such a large vessel lost control and how the huge structure of the bridge crumbled so quickly.   On today's edition of the Sky News Daily, Leah Boleto speaks to our US Correspondent Martha Kelner in Baltimore and our Science Correspondent Thomas More. Plus, Ben Schafer, a structural engineer at Baltimore's Johns Hopkins University explains why the bridge fell so quickly.   Senior producer: Annie Joyce Assistant producer: Iona Brunker  Editor: Wendy Parker