Complex sentence: After the disaster of the Dieppe raid, Bernal was determined that these mistakes not be repeated in Operation "Overlord", and demonstrated the advantages of an artificial harbour to the participants of the Quebec Conference in 1943 as the only British scientist present.
Split into simpler sentences: After the disaster of the Dieppe raid, Bernal was determined that these mistakes not be repeated in Operation "Overlord". He demonstrated the advantages of an artificial harbour to the participants of the Quebec Conference in 1943, as the only British scientist present.