 Attacks on the German submarines continued for the next six days . On the morning of 18 July a German reconnaissance aircraft spotted the Home Fleet , but the German Naval Command Norway assessed that it was heading north @-@ east to launch another attack . Accordingly , Group Trutz was ordered to sail north , and four more submarines sortied from Narvik to guard the approaches to Alten and Vest fjords . In the evening U @-@ 968 , one of the four boats that had sailed from Narvik , was attacked twice by Liberators ; she shot down the first attacker but was damaged by the second and had to return to port . U @-@ 716 also suffered severe damage from a Liberator attack at 19 : 15 on 18 July but managed to return to Hammerfest . At about 23 : 00 that day U @-@ 716 was seriously damaged by a Short Sunderland but also survived . Three other submarines were attacked on 20 July but only one suffered any damage . Following these actions the commander of submarines in the Norway area decided to dissolve Group Trutz as it was too vulnerable to air attack ; all but four of the surviving submarines returned to port and the remaining boats were ordered to sail north so that they were out of range of the British aircraft . The final attack on the submarines of the former Group Trutz was made on 23 July when a No. 330 Squadron Sunderland damaged U @-@ 992 near Vestfjord . 
