of machinery to drive During this period Buggisch's team conducted research into the field-rewirable reflector, () which lead to the Enigma Uhr device. Another device which was created to increase the security of Enigma was the Lückenfüllerwalze, or gap-filling wheel, that was built by Fritz Menzer. This was a device for varying turnover of wheels by means of adjustable plugs on the perimeter. The effort to improve the Enigma was a result of the implications of what was known Der Fall Wicher or Case Wicher. This was German knowledge, or supposed knowledge, that the Enigma cipher machine and therefore its own key processes, were not secure and had already been read by the Allies. The Fall Wicher was the knowledge that was received from two Polish officers being held in a concentration camp who had been captured in France in 1940. The two officers had been repeatedly interviewed in the intervening years of the war and revealed nothing to their German interrogators. Finally, in late 1943, early 1944 when the war had turned against Germany they had volunteered the information that the Enigma device had been broken by Polish cryptanalysts several years before the war, confirming German suspicions. Mid 1944 to April 1945 During this period Buggisch was attached to the Communications Experimental Station, located in a cave in Staats. The station was part of the Army Ordnance Branch, department WA Pruef 7, Section IV, Referat A from June 1944. He worked on the mathematical treatment of ciphony systems. During this period Buggisch also worked almost exclusively on Russian X2 ciphony device. He also worked on the T52 teleprinter frequency Undulator device. Later work was the theoretical investigations into the construction of Tigerstedt keys, from a cryptographic device constructed by Eric Tigerstedt. Autumn 1944 In Autumn, Buggisch's attachment to WA Pruef 7 was suspended, and he was transferred from AgN/NA to OKW/Chi Chi IV Analytical Cryptography (). This move was specifically designed to enable him to attend the Chi conference in Berlin at the instigation of Major General William Gimmler, (). Gimmler was the Chief Signals Officer and Chief of the Armed Forces Signal Communications Office. The Chi conference took place over a period of three months from November 1944 through January 1945. Gimmler had insisted on them, although the mathematician Erich Hüttenhain who also worked an OKW/Chi, was against them, and felt it was a waste of time to