At 23.31 hours on 22 Aug, 1941, U-564 fired a salvo of four torpedoes at the convoy OG-71 west of Aveiro, Portugal and observed four different detonations and three columns of fire, later lifeboats were seen. Suhren thought that he had sunk two ships and damaged two others. However, only two ships were hit and sunk, the Empire Oak and Clonlara.

The master, three crew members and four gunners from the Empire Oak (Master Frederick Edward Christian) were picked up by HMS Campanula (K 18) (LtCdr R.V.E. Case, DSC), transferred to HMS Velox (D 34) (LtCdr E.G. Ropner DSC) and landed at Gibraltar on 25 August. 13 crew members were lost.
On 19 August, the Empire Oak had picked up six survivors from Aguila and eleven survivors from Alva. The survivors from Aguila died when this ship was sunk, while the other survivors were also rescued by the corvette.