Columbia subject headings:
Great Britain--History, Naval--20th century.
Merchant marine--Great Britain--History--20th century.
Navigation--Great Britain--History--20th century.
Harvard subject headings:
Great Britain--History, Naval--20th century.
Merchant marine--Great Britain--History--20th century.
Navigation--Great Britain--History--20th century.
Princeton subject headings:
Great Britain--History, Naval--20th century.
Merchant marine--Great Britain--History--20th century.
Navigation--Great Britain--History--20th century.