midnight
Kapitan Schwalbe had taken the advantage of the opportunity of a few hours ' sleep . Under-officered and undermanned , the strain on the personnel was a severe one . It was only on rare occasions that Schwalbe could in future descend from his post in the conning-tower . At midnight , according to custom , the submarine called up her consorts by wireless . Judging by the previous attempt it seemed a useless task , but to the Operator 's surprise he received a reply from U77 , which was then lying off the Scillies . Kapitan Schwalbe , aroused from his sleep , eagerly awaited the decoding of the message . It was to the effect that the commander of U77 had received information that H.M.S. _ Tremendous _ , one of the earlier Dreadnoughts , was leaving Gibraltar for Rosyth .