Before revision: Date Event Oct. 15, 1941 Introduction of the "Neptune" key network for the battleships with the M4 November 1941 Introduction of the address book procedure to conceal position details Feb. 1, 1942 Introduction of the M4 now also for the U‑boats (initially only Greek roller β) Oct. 30, 1942 HMS Petard captures second edition of the weather shortcut key from U 559 12. Dez.
After revision: Date Event October 15, 1941 Introduction of the "Neptune" key network for the battleships with the M4 November 1941 Introduction of the address book procedure to conceal position details February 1, 1942 Introduction of the M4 now also for the U-boats (initially only Greek roller β) October 30, 1942 HMS Petard captures second edition of the weather shortcut key from