 Complete the following phrase:  Having earned a mention in dispatches for his Zeal and intrepidity in the boat action with Potomac, Birchall was made a commander in 1797 and by 1798, had commissioned the lightly armed but fast troopship, Hebe. In May, she was serving in a squadron under Home Popham, sent to prevent the movement of a large number of enemy barges from Vlissingen to Dunkirk. The large flat-bottomed boats were to be used to convey troops across the Channel for 