An illustration of the "Dowding System" of defensive air control, from a 1941 Air Ministry pamphlet. In the lower left is the overall control system at Fighter Command HQ at Bentley Priory, shown dis
<p>UK Air Ministry<br></p>
(Life time: 70 years from publication (see <a rel="nofollow" class="external free" href="http://www.caret.cam.ac.uk/copyright/Page171.html">http://www.caret.cam.ac.uk/copyright/Page171.html</a>))
<p><b>Original publication</b>: Air Ministry pamphlet<br></p>
<b>Immediate source</b>: <a rel="nofollow" class="external free" href="http://ww2today.com/2nd-april-1941-the-battle-of-britain-defined">http://ww2today.com/2nd-april-1941-the-battle-of-britain-defined</a>