When after World War II the passenger aircraft replaced the passenger liner for travel across the Atlantic and Pacific Oceans, good weather forecasting became necessary. Actual weather observations taken on a regular basis had to be performed from various areas of these two oceans in order to develop forecasts. The world's major political powers came together on this idea in London England and as a result, Ocean Weather Stations (OWS) were created in 1946. For these there were three major objectives:
- to provide positional information for long range, propeller flights over the Pacific and the Atlantic;
- weather forecasting and measurement of winds aloft;
- for long range aircraft flight planning based on weather observations.
The ships were not only to provide surface weather observations but also of the upper air pressure, temperature, humidity, wind direction and speed. They were also equipped for search and rescue operations for both ships and aircraft.

Stations were designated at various positions throughout both oceans and the positions chosen so as to fill the gaps where there were no shipping lanes and from where no weather reports came. Each position was assigned a letter for identification purposes. The first half of the alphabet became the Atlantic areas and the second half, Pacific areas. Canada and the United States were to share station 'B'. Since this undertaking became the responsibility of the International Civil Aviation Organization (ICAO) the International Telecommunication Union (ITU) assigned a block of call signs for their use. This block spanned from 4YA to 4YZ.