Today, it seems that a whistle or horn on a ship is used only to give passing signals, to request the opening of a few bridges, to salute fellow ships or tourists on shore, and occasionally to sound a warning of danger. Few ship fans realize the beautiful chime whistle, such as that on the ROBERT C. NORTON, was developed not only because of its pleasing sound, but also because the ability of the whistle to make itself heard over long distances and in any weather could mean the difference between a safe passage and an accident involving the loss of men and ship.
In the days before radio communications ship to ship and ship to shore, the steam whistle was virtually the only method of communication and a very intricate series of signals had to be worked out for almost every one of the situations in which a ship might find herself. There were signals for calling tugs, for opening bridges, for picking up and dropping barges, for finding the right dock, for comparing courses with passing steamers and for simply reporting passage to such stations as that which was located at the Straits of Mackinac,
For instance, to quote the Lake Carriers' Association booklet of 1942, "...if when a vessel is approaching the Duluth entrance she is signalled by the local Great Lakes tugs by its fleet and vessel signal, she should reply with similar signals and with the expectancy of receiving a change of orders, as follows: "Two long blasts from tugs (- -) means to go to Superior entrance. (The vessel will always be a light one and she will understand that she is to load at the Great Northern Ore Docks.) Two long and one short (- -.) means that she is to turn around and go back to Two Harbors. One short, one long, one short (.-.) means that she is to turn back and go to Ashland for cargo. This is the same signal that is given at Two Harbors to indicate that the vessel is to return to Ashland,"
A ship's personal signal consisted of a series of blasts to indicate the fleet, and another to indicate the particular ship. In the case of the Pittsburgh Steamship Co., there were so many ships that each was also assigned "class" to be given between the fleet and name signals. There follows a portion of the Pittsburgh whistle signal list for 1942.
Reproduced for the Web with the permission of the Toronto Marine Historical Society.