The outbreak of the Second World War, however, far from putting the Channel tunnel completely out of sight, revived the issue, for a time, anyway. In November 1939 the French Chamber of Deputies passed a resolution calling for the construction of a tunnel; early in 1940, Prime Minister Neville Chamberlain—the son, incidentally, of Joseph Chamberlain, who as president of the Board of Trade had ordered the tunnel workings stopped back in the eighties—turned the tunnel project down again in a parliamentary reply. The retreat from Dunkirk gave pro-tunnel and anti-tunnel people the opportunity of putting forth their arguments about the tunnel once more, with some variations—with the pro-tunnelers claiming that a Channel tunnel might have enabled the British Expeditionary Force to keep a bridgehead in France, and the anti-tunnelers countering that the same tunnel would have given German paratroopers the opportunity of seizing the English end and using it as a bridgehead for the invasion of England. Then, after the fall of France, when the Germans were busily making preparations for the invasion of England, the question arose among the British military as to whether the enemy might not just possibly attempt to reach England by surreptitiously tunneling underneath the Channel. As a consequence, the War Office called in an eminent British civil engineer, the late Sir William Halcrow, and asked him to make a study of the question of whether the Germans could pull off such a feat. "We examined the situation quite carefully and concluded that, provided we kept reasonably alert, the Germans could not dig the tunnel without being detected," an engineering colleague of Sir William Halcrow's on the survey said a while ago. He added, "Their difficulty would lie in the disposal of the spoil. They couldn't get rid of it without our seeing from the air that something peculiar was going on. If they tried to dump the spoil into the sea at night it would have to be done at the turn of the tide, and the chalk would leave a cloud in the sea that would not be dissipated by daylight. If they pulverized the spoil, converted it into a slurry, and pumped it well out to sea, we would be able to spot the chalk cloud too, and even if they tried other means of dispersing the spoil the very process of dispersal would call for such extensive installations that we would soon be on to them."