Saalwächter was born in Neusalz an der Oder, Prussian Silesia, as the son of a factory manager. He entered the Kaiserliche Marine as a Seekadett on 10 April 1901, and was trained on and. On 29 September 1904 he was promoted to Leutnant zur See. Saalwächter then served with Bordkommando units, first with the 2. Matrosen-Division, then on with the 2. Werft-Division. He was promoted to Oberleutnant zur See on 10 March 1906; until 1908, he served with the 2. Torpedo-Division as adjutant to the I. Abteilung. Saalwächter also served on. Saalwächter served on in 1910 and later on as Flaggleutnant to Vice AdmiralHugo von Pohl, commander of the I. Marine-Geschwader. Saalwächter was promoted to Kapitänleutnant on 10 April 1911 and joined the admiralty in Berlin. He remained in the admiralty until 1915, with his last position there being head of the signal section in the operations department. In 1912 he received the Order of the Red Eagle.
World War I
On 1 April 1915 during World War I, Saalwächter became Flaggleutnant on, the flagship of the High Seas Fleet. In February 1916 he transferred to the U-boat service. After graduating from submarine school, he commanded,, and from September 1916 to March 1918. He was awarded for his success with the Iron Cross 1st Class and the Knight's Cross of the House Order of Hohenzollern.
Interwar era
In 1920, Saalwächter was named a Korvettenkapitän of the Provisional Reichsmarine. He also served on as an admiralty officer. After a leave of absence, Saalwächter joined the Marineleitung in the Personnel Department on 17 May 1920. From 15 October 1923 till 31 March 1925 he served as 1. Asto in the staff of the Commander of Naval Forces. On 24 September 1926 he took command of the light cruiser, and, a year later, under promotion to Fregattenkapitän of the battleship. On 2 October 1933 Saalwächter was named inspector for naval instruction. During the following five years he had a strong influence on the development of the young officer corps. He was promoted to Vizeadmiral on 1 April 1935 and Admiral on 1 June 1937. Saalwächter was named Commanding Admiral of Naval Station North Sea at Wilhelmshaven, one of the highest positions in the Kriegsmarine at the time, on 28 October 1938. On 2 March 1939, Saalwächter sent a report to the Naval High Command in which he openly discussed the acquisition of bases in Norway. The report stressed both the dangers to Germany of British dominance in Norwegian waters and the favourable change in the geo-strategic position that a German occupation of Norway would bring about.