The direct detection of towns and individual buildings had
been a specific nuisance to AI systems working at 1.5 m and
was always referred to as 'ground clutter'. Little or no definition
in the ground return was possible with such a system.
The issue of inaccurate bombing caused by poor target identification
had been highlighted in the Butt
report. The matter was discussed in July 1941 and
again in late 1941. The direct results of these findings was
the rapid development and subsequent introduction of the GEE
radio beacon location system; ready for operational use by
March 1942.
Furthermore, it was pointed out that the majority of industrial
targets would be steel-framed buildings. The idea of modifying
the newly introduced 10 cm AI equipment with a downward facing
antenna array was investigated.
Both spiral and helical scanning dishes were evaluated but
the first trials took place very quickly with P.I.Dee in charge.
By March 1942 a prototype unit was installed in a specially
built Halifax with a Perspex dome under the belly of the aircraft)
for trials to be undertaken.
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