Pelham Aldrich, son of Dr Pelham Aldrich of Mildenhall, Suffolk, England, entered the Royal Navy as a youngster in 1859 and was promoted to lieutenant in 1866. From 1872 to 1875 he served with the rank of first lieutenant in the Challenger deep sea exploring expedition. After marrying Edith C. Isaacson in 1875 he sailed that same year as first lieutenant on the Alert in the Arctic Expedition of 1875-1876. The next year he took command of HMS Sylvia, one of several surveying ships in commission on foreign surveys during the late nineteenth century. In 1884 he sailed from the Cape of Good Hope northwards along the west coast to Walvis Bay (Namibia), making a hydrographic survey of the coast north of the Orange River. (An earlier survey of this coast was made by Captain T. Alexander* in 1795-1796.) Part of the results of Aldrich's survey were summarised in five manuscript charts, the most important being those of Sandwich Harbour and Hottentot Bay. He also provided a detailed description of the coast and offshore islands, with a critique of, comments on, and additions to the relevant portions of the African Pilot (Part 2, 1875). The ship lent her name to a conspicuous double-peaked hill, Sylvia Hill, first described and plotted by the expedition in latitude 25º 10' South.
Under Aldrich's command the Sylvia performed another historically significant voyage in April 1885, when she transported an Anglo-German commission up the west coast to inspect disputed territory at Walvis Bay, Sandwich Harbour, Luderitz, and the guano islands. The results were published in the Proceedings of the Angra Pequena and West Coast Claims Joint Commission in 1885.
Aldirch's subsequent work led to brief articles on Christmas Island and on "Barometric oscillations" in the journal Nature in 1888 and 1889 respectively. He was promoted to Rear-Admiral in 1898, Vice-Admiral in 1903, and Admiral in 1907. From 1899 to 1902 he was Admiral Superintendent of Portsmouth Dockyard and in the latter year was honoured as a Commander of the Royal Victorian Order (CVO). After his retirement in 1908 he lived at Great Bealings, Suffolk, England. The crinoid (feather star, related to sea urchins) Bathycrinus aldrichianus was named in his honour by Sir Charles Wyville Thomson*.