Complex sentence: It was sighted by German aircraft on 30 June and 2 July; however QP13 was not attacked, since the German tactic was to concentrate on eastbound (laden) convoys, rather than westbound convoys in ballast.
Split into simpler sentences: It was sighted by German aircraft on 30 June and 2 July. However QP 13 was not attacked, since the German tactic was to concentrate on eastbound (laden) convoys, rather than westbound convoys in ballast.