Black Diamond Steamship Company (BDSC) operated passenger and cargo liners from New York City to Rotterdam and Antwerp.

Prior to the United States' entry into World War II, the nation's neutrality policy ended much of the lines trade.

Dockendorff stepped down as a principal executive in 1934, selling the only one of the company's 21 ships not owned by the government: New Britain, which he had bought in 1918.

The most common armament mounted on these merchant ships were the MK II 20mm Oerlikon autocannon and the 3"/50, 4"/50, and 5"/38 deck guns.

[3] American Diamond Line was started at the end of World War I in 1919, by the United States Shipping Board.

Black Diamond Steamship Company had weekly routes to Charlottetown, Montreal, Sydney, and St. John's.