A cursory glance online did not lead me to his biography, but a few facts were gleaned which I hope are of some benefit to your search:
Walter Thomas (1894-1971) - a Liverpool marine painter and illustrator. He painted in both oil and watercolour providing subjects that could be translated into poster art and other promotional projects.
He worked for the Liverpool printing firm of Turner and Dunnett as assistant to Odin Rosenvinge, one of the most prolific of the poster artists. Clients of the firm included the major shipping companies Blue Funnel, Cunard, Elder Dempster and White Star Line.