Dannreuther entered the Navy as a cadet in 1885 and trained in HMS BRITANNIA. In 1887 he went to sea as midshipman in HMS GARNET which was posted to the East Indies Station. He was in HMS INFLEXIBLE, Mediterranean, in 1891, after which he specialized in navigation. From 1892 to 1894 he served in HMS IRIS and HMS FOXHOUND in home waters. He was appointed lieutenant of HMS MELITA in 1894, serving in the Mediterranean and the Red Sea, and took part in the Dongola expedition of 1896. Dannreuther was in HMS LEANDER in the Pacific from 1897 to 1900. He subsequently served in HMS ARIADNE and HMS HOOD, Mediterranean, HMS LEVIATHAN, China Station, and HMS BACHANTE, HMS ROXBOROUGH and HMS VINDICTIVE in home waters. He was promoted to commander in 1905 and served in HMS LEVIATHAN and HMS AMPHITRITE on manoeuvres, 1895-1899 the Home Station from 1906 to 1907 and in HMS KENT on the China Station, 1907 to 1909. In 1911 he was appointed to command HME INTREPID, one of the early minelayers, and from 1914 to 1915 was engaged in the same capacity on HMS MARS. In 1915 he commanded HMS KINFAUNS CASTLE at the Cape of Good Hope and, from 1916 to 1919, HMS PATUCA, on convoy escort duties in northern waters. He was promoted to captain in 1918. Dannreuther's last appointment was as one of the Assistant Directors of Naval Intelligence from 1919 to 1921.
The papers were presented in 1963 by Rear-Admiral H.E. Dannreuther, excepting the letters from Captain Dannreuther to his mother which were presented by Captain H.M. Dannreuther in 1973. The collection contains logs, 1887 to 1891, night order books, 1911 to 1917, notebooks, 1890 to 1891, diaries, 1887 to 1958, and remark books, 1893 to 1912. There are numerous letters from Dannreuther to his mother written between 1885 and 1919, except for the years 1909 to 1914, and official documents relating to the ships under his command. In 1977 and 1982 Captain Hubert Harold Dannreuther presented various additional papers to the Museum. Further papers were purchased from J & L Spake in 1984.