Information had reached the British Secret Intelligence Service (SIS) about German weapons development since the Oslo report of November 1939, from Royal Air Force (RAF) photo-reconnaissance photographs taken from 22 April 1943 and eavesdropping on Lieutenant-General Wilhelm Ritter von Thoma, who expressed surprise that there had been no rocket bombardment of Britain. Other prisoners of war gave various and sometimes fanciful accounts. Information also came from Polish intelligence, a Danish chemical engineer and from Leon Henri Roth and Dr Schwagen Luxembourgish (forced labourers) who had worked at Peenemünde and smuggled out letters describing rocket research, giving conflicting accounts of the size, warhead range and means of propulsion of the device. Despite the confusion, there was little doubt that the Germans were working on a rocket and in April 1943, the Chiefs of Staff warned operational HQs of the possibility of rocket weapons. Duncan Sandys was appointed by Winston Churchill to lead an inquiry to study the information and report on counter-measures.