The house flag of the Atlantic Steam Navigation Co. Ltd, London. A swallow-tailed pennant with a pale blue border. The flag is made of a wool and synthetic fibre bunting. It has a cotton hoist and is machine sewn. A rope and two Inglefield clips is attached. The commodore's flag was a similar design with a miniature of the house flag in the upper canton of the hoist.

Using the name of an earlier company in operation from 1858 to 1859 carrying Irish emigrants to America, the Atlantic Steam Navigation Co. was started in 1936 by Lieutenant-Colonel Frank Bustard. A pioneer of roll-on/roll-off ferries, the company owned no ships until after the Second World War when it acquired ex-navy landing craft. It lost its independent identity in 1974 when it was acquired by Townsend Thoresen and is now part of P&O.