The strength required for defences against air raids was explained in an address given to the Southland branch of the New Zealand Institution of Engineers by Mr W. H. Gregory. He said it was estimated that the striking velocity of a very heavy bomb was 1200 feet a second, while small incendiary bombs would reach a velocity of about 400 feet a second. The estimated vertical penetration of a 20001 b bomb into the ground would not exceed 60 feet. Actual tests carried out showed that a 5001 b bomb would penetrate 2ft 6in of concrete and about 20 feet of sand or earth.
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Wairarapa Times-Age, 28 October 1939, Page 10
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104Untitled Wairarapa Times-Age, 28 October 1939, Page 10
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