North Atlantic weather war

The North Atlantic weather war occurred during World War II. The Allies (Britain in particular) and Germany tried to gain a monopoly on weather data in the North Atlantic and Arctic oceans. Meteorological intelligence was important as it affected military planning and the routing of ships and convoys. In some circumstances, visibility was necessary (photographic reconnaissance and bombing raids) and in others concealment (keeping ship movements secret or suppressing enemy air activity). D-day planning was greatly affected by weather forecasting; it was delayed by one day in the expectation that a storm would blow out and sea conditions would be acceptable. British sources of data included ships at sea and the weather stations at Valentia Observatory and Blacksod Point, in neutral Ireland; German use of weather ships also exposed their secret Enigma codes.