When the D-day landings took place on 6 June 1944, the U-boats were ordered into action with the awareness that the western flank of the invasion would be well protected at sea. Operational experience with the snorkel was too scant to devise instructions for its use. The narrow, shallow, waters of the English Channel provided few opportunities for charging the batteries. Dönitz feared the task was impossible. The "Holzbein" group based at Brest, sent 15 submarines into action against the Cherbourg peninsula landings part of a 36-strong flotilla. Only eight had snorkels. The seven non-snorkel boats were ordered to attack on the surface. The BdU war diary entry on 6 June 1944 states that "for those boats without schnorchel this means the last operation." Of the 15, only five got near to the invasion fleet. Five of the snorkel boats survived. In exchange for 10 U-boats with the survivors damaged, two frigates, four freighters, and one tank landing ship were sunk. 22 U-boats were sunk from 6–30 June 1944. On 5 July 1944, the Allied Operation "Dredger" permitted hunter-killer groups to roam the Western Approaches and Biscay making it a "no-go area" for U-boats. U-boat operations against Normandy landings were a fiasco. Dönitz and the high command had been ignorant of the true scale of the naval D-day effort. Dönitz claimed his men sank five escorts, 12 merchant ships and four landing craft for 20 submarines and 1,000 men, of whom 238 were rescued. Dönitz's claims underplayed German losses, which were, in fact, 41 submarines from 82 in France, a 50 percent loss rate.