Two were killed, and Philby was slightly wounded. For his courage under fire, Franco presented him with a medal, further establishing his false anti-Communist credentials. None of the four's loyalty to the Soviet Union was affected by the Stalin-Hitler Pact of 1939, since they were clever enough to realize that Stalin's embrace of Nazi Germany was a temporary expedient. Blunt joined MI5, now allowing him to expand his services beyond recruiting and giving him opportunities to transmit secret documents to his KGB control. But it was between 1940 and 1945 that the four did most of their first serious damage to Britain and the United States.
Authorities differ as to which of the four was the most effective for the Russian cause.
Burgess and Blunt contributed to the Soviet cause with the transmission of secret Foreign Office and MIS documents that described Allied military strategy. Although he did not transmit technical data on the atom bomb, he reported on its development and progress, particularly the amount of uranium available to the United States. This knowledge alone gave the Soviet scientists the ability to predict the number of bombs that could be built by the Americans. Coupled with the efforts of Alan May Nunn and Klaus Fuchs, who provided scientific information, Maclean's reports to his KGB controller helped the Soviets not only to build the atom bomb, but how to estimate their nuclear arsenal's relative strength against that of the United States. Kim Philby carried out a variety of assignments.