 The rank of admiral-general was reserved for the stadtholder, but at the time, no-one held that appointment.The main function of De Ruyter's squadron was to convoy outbound or returning Dutch merchant ships through the English Channel, where they were vulnerable to attacks from English ships based at Portsmouth or Plymouth.In August 1652, a convoy of around 60 Dutch merchant ships left the Netherlands for the Mediterranean, initially with an escort of 10 warships.