The timing of the first raid was influenced by advice given by Sir Malcolm McAlpine, the chairman of the construction company Sir Robert McAlpine, who suggested that the Watten site should be attacked while the concrete was still setting. On 27 August 1943, 187 B-17 Flying Fortresses of the US 8th Air Force attacked the site with devastating effect. The fortified train station on the north side of the bunker was especially badly damaged, as concrete had just been poured there. Dornberger later wrote that following the attack the site was "a desolate heap of concrete, steel, props and planking. The concrete hardened. After a few days the shelter was beyond saving. All we could do was roof in a part and use it for other work." The bombing killed and injured hundreds of the slave workers on site; although the Allies had sought to avoid casualties by timing the raid with what they thought was a change of shifts, the shift pattern had been changed by the Germans at the last minute to achieve the day's work quota.