"Keith Willshaw" wrote:

Ground controlled approach using precision radar was pioneered by
the RAF in WW2. Arthur C Clarke wrote an excellent book
called 'Glide Path' about the project (on which he worked)

The Germans had the Lorenz blind landing system and both the
Americans and British had similar systems in use pre war

In 1930 the American Bureau of standards introduced the first directional
guidance system using a transmission on 330 kHz with two tones
that were transmitted of 65 and 85.7 Hz.
In the aircraft receiver, these were received, applied to filters, detected
and used to energise a centre zero meter. The edge of the airfield was
defined by the cone of silence over a simple beacon modulated at 40 Hz
F. Dunmore improved on the system by adding a VHF signal on 93 MHz that
was transmitted from a location at the upwind end of the runway, if the
aerial was mounted at a suitable height, then a line of equal field strength
would approximate to the require vertical guidance pattern.

The first blind landing using this system took place in 1931

So, in a nutshell GCA was the primary precision approach
and NDB was the primary non-precision approach used in WW2?

-Mike Marron