In volume II of "The Strategic Air Offensive against Germany" (1961) part of the official "History of the Second World War", Webster and Frankland wrote that Dornberger thought that the bombing delayed the A4 (V2) project by four to six weeks, which had been followed by many later accounts but that this was anecdotal. The official historians wrote that the transfer of production to the Harz mountains and testing to Poland must have caused some delay in remedying the numerous design failings of the device and that the killing of Thiel and Walther might have made things worse. The attack on Peenemünde and other sites might have delayed the V2 offensive by two months. Although research and development continued almost immediately and test launches resumed on October 6, plans for some German V-2 facilities were changed after Hydra; the unfinished production plant for V-2s was moved to the Mittelwerk.