The attack was reported up the chain of command to both Erwin Rommel and Dwight D. Eisenhower on 29 April. Eisenhower was enraged that the convoy was sailing in a straight line and not zig-zagging, that the attack reduced reserves of LSTs, that it indicated to the Germans that the Allies were nearly ready to invade, and that ten American officers with knowledge of the invasion were missing. The missing officers had BIGOT-level clearance for D-Day, meaning that they knew the invasion plans and could have compromised the invasion should they have been captured alive. As a result, the invasion was nearly called off until the bodies of all ten victims were found. He ordered that all the officers’ bodies, and any incriminating papers they might have had, be found. The ten American officers were from the 1st Engineer Special Brigade; they knew when and where the Utah and Omaha landings were to take place, and had seen the amphibious DUKWs that were to take the Rangers to below Pointe du Hoc. Merely knowing that exercises were taking place at Slapton was of interest to the Germans; the historian Stephen Ambrose suggests that the insistence in May by Hitler that the Normandy area be reinforced was because "he noticed the similarity between Slapton Sands and the Cotentin beach".