The house flag of Ulster Steamship Co Ltd, Belfast. A blue rectangular flag bearing a white shield with the red hand of Ulster dripping blood. The white initials 'USS Co' placed near the hoist. The flag is made of a wool and synthetic fibre bunting. It has a cotton hoist and is machine sewn. A rope and toggle is attached.

The Ulster Steamship Company was registered in 1877, the company ran services to the east coast of Canada, the Far East, Europe and Baltic Ports. Voyages to New Orleans started in 1896 and the company began carrying a limited number of passengers at about the same time. In 1917 the Irish Ship-owners Company Ltd, (Thomas Dixon & Sons, Belfast) known as Lord Line, was taken over. They had run sailings between Belfast, Dublin, Cardiff and Baltimore, Rotterdam to Galveston, and Cardiff to Montreal and Quebec. Lord Line continued these services as a subsidiary.
Agreement was reached in 1919 between the Ulster Steamship Company, Palgrave, Murphy & Company, Dublin and Hudig & Veder NV Rotterdam, to form a working partnership and to pool vessels. There were limited inter-fleet sales of vessels between the three partners. Following the changes of ownership and the creation of the Republic of Ireland the company was re-registered in Belfast in 1924. On the opening of Great Lakes to foreign deep sea vessels in 1959, the company established a new service. Ulster Steamship Company acquired the shares of Donaldson Line in 1967 and the company traded under the name of Head-Donaldson Line. In 1979 the last ship was sold and the firm was absorbed into Canadian Pacific Operations.