sentences:  On the morning of April 11, 1975, helicopters from the United States Seventh Fleet began circling the VPN transport ships, but they were allowed to move on as the disguised North Vietnamese ‘fishing trawlers’ were mistakenly identified as ships from Hong Kong.After the American helicopters flew away, the North Vietnamese continued sailing towards Southwest Cay.On the night of April 13, the three ships were closing in on Southwest Cay from three different directions.