It was installed by US ambassador, Joe Kennedy, in 1938 and was intended to inspire his children — including a young JFK, who visited his father here in the late 1930s — to achieve power and accustom them to its trappings.

Source: https://propertylistings.ft.com/propertynews/london/7040-grosvenor-squares-original-us-embassy-building-gets-the-poshest-and-most-discreet-of-residential-makeovers.html