"Thomas Rainsborow (alias Rainsborough or Rainborowe) was a son of a distinguished sea captain, William Rainsborow (died 1642), and was himself bred to the sea. One of Thomas' sisters married John Winthrop (1588-1649), Governor of Massachusetts, and another married the governor's fourth son, Colonel Stephen Winthrop (1618-58). Thomas had a brother, who was another parliamentarian, Captain William Rainsborow, who was in Colonel Thomas Sheffeild's Regt. of Horse of the New Model Army, and became a major by July 5th, 1647, but was dismissed in 1649.
In 1643 Thomas Rainsborow was in command of the ship 'Swallow', and took a royalist ship that was carrying reinforcements to the King. Then as captain of the ship 'Lion' he landed 100 (possibly 180) of his crew to help Lord Fairfax's defense of Hull, and while himself leading a column of 500 musketeers, was captured in the great sally which terminated the siege (Oct. 11th, 1643). In his account of the fight Lord Fairfax described Rainsborow as a Colonel, which he was continually described as, with his later service as a colonel being all on land."