Number of planes by radar 1940

In the Secret war: To see for a hundred miles it is mentioned that the shape of the bombers flying on the radar screen revealed the number of the bombers in formation.

Can anyone confirm this? Know any examples of this? Tanx!

 

Aircraft of the WW 2 period were not designed with particular regard to their radar signature (obviously).
Determining the size of a group of aircraft on radar depended on the wavelength and beam width of the particular radar in use. To 'see' individual aircraft they had to be far enough apart that the beam and wavelength returned each as a seperate entity. When aircraft flew in larger groups the signal return was a composite of all the returns in the group rather than a bunch of individual returns.
A good operator could determine the approximate size of an aircraft formation by the strength of the return at a particular range compared to the known or expected return of a single aircraft at the same range.
On two dimensional systems (like CH), altitude was approximated by use of a "fade chart." This showed the vertical lobe pattern and the gaps that occured within it (this looks something like a stack of flashlight beams). As the target aircraft flew through the beam it could disappear for a short period as it entered a gap in the coverage. The operator could use the fade chart to determine at what range it disappeared and get a rough height determination from the chart.
So, it really isn't the "shape" of the formation but rather its proximity that determines the size of the return.

 

Thanx T.A.!

I´d think that sending the suitable number of fighters to the right address was of the highest importance. So could an operator ruin the fighter pilots´ actions by not reading the strength of the return correctly? And thus just the radar signal in itself was not all you needed to know to win the war in the air?

 

It was important for the operator to give several pieces of accurate information. These included the range, speed, altitude and, approximate strength of the raid. Altitude is particulary important. If this was misestimated, particularly if lower than the actual height the intercepting fighters could arrive in the target area with insufficent altitude making it difficult for them to climb to intercept.
The strength of the return was less important. Since it was only an estimate at best...something like "a small raid" or, 'a large raid"....was likely to generate roughly the same response in terms of number of fighters sent regardless of the actual exact number of aircraft in the raid.
Speed, range and, bearing are also vital information pieces. These determine the interception point and how the interception is handled. This information can also be useful in alerting ground defenses and potential targets about the attack, allowing them to prepare for its arrival.
In the strategic bombing campaign against Germany both the US and British regularly made great efforts to confuse the German defense system using deception methods to conceal the target(s) to be attacked. Small diversionary raids, deception jamming and, route planning to make it appear one target is to be attacked with a last minute turn onto another course attacking a different target are examples of this.
Even in the Battle of Britain other methods were still in use to gain information on enemy attacks. Ground observers were still used to confirm and give exact numbers of attacking aircraft in addition to radar. The primary use of radar was to give very early raid warning that allowed the defender more time to reply.