The first 12,000-lb Tallboy bombs developed by Barnes Wallis were used on this night by 617 Squadron in a raid on a railway tunnel near Saumur, 125 miles south of the battle area. The raid was prepared in great haste because a German Panzer unit was expected to move by train through the tunnel. The target area was illuminated with flares by 4 Lancasters of 83 Squadron and marked at low level by 3 Mosquitoes. 25 Lancasters of 617 Squadron then dropped their Tallboys with great accuracy. The huge bombs exploded under the ground to create miniature `earthquakes’; one actually pierced the roof of the tunnel and brought down a huge quantity of rock and soil. The tunnel was blocked for a considerable period and the Panzer unit was badly delayed. No aircraft were lost from this raid.