The date of Myngs's birth is uncertain, but probably somewhere between 1620 and 1625. It is probable that he saw a good deal of sea-service before 1648. He first appears prominently as the captain of the Elisabeth, which after a sharp action during the First Anglo-Dutch War brought in a Dutch convoy with two men-of-war as prizes. From 1653 to 1655 he continued to command the Elisabeth, high in favour with the council of state and recommended for promotion by the flag officers under whom he served.