At that stage of the war, Allied and German intelligence operations were heavily mismatched. Through the signals work at Bletchley Park, many of the German lines of communication were compromised since intercepts, codenamed Ultra, gave the Allies insights into how effectively their deceptions were operating. In Europe, the Allies had good intelligence from resistance movements and aerial reconnaissance. By comparison, most of the German spies sent into Britain had been caught or had handed themselves in and turned into double agents (under the XX System). Some of the compromised agents were so trusted that by 1944, German intelligence had stopped sending new infiltrators. Within the German command structure internal politics, suspicion and mismanagement meant intelligence gathering had only limited effectiveness.