In 1936, Forbes, Helen Gwynne-Vaughan and Kitty Trenchard launched the Emergency Service, to train women and organise them to be prepared in case of war.

Early in the war she is said to have allowed the house to be used as a place for senior militarily personnel to have a few days respite – Field Marshal Sir Bernard Montgomery is thought to have been among the guests.

[5] At one time engaged to a cousin who died mountaineering, she was unmarried until 1966, when she and Sir Robert Alexander Watson-Watt, who is credited with developing radar, married in London.

They lived together in London in the winter, and at "The Observatory" (Trefusis Forbes' summer home in Pitlochry, Scotland) during the rest of the year.

The couple met for the first time back during World War II when the WAAF was responsible for managing radar installations.