Complex sentence: Previously, this escape attempt had been planned for the summer as good weather was a large factor of success but in early 1944, the Gestapo had visited the camp and ordered increased efforts in detecting possible escape attempts.
Split into simpler sentences: Previously, this escape attempt had been planned for the summer as good weather was a large factor of success. However, in early 1944 the Gestapo had visited the camp and ordered increased efforts in detecting possible escape attempts.