The bulk of this sub-collection consists of letters written by Field to his wife when he was captain of HMS PENGUIN surveying in the Pacific, 1896-1899; and from HMS RESEARCH surveying in home waters, 1900-1903. The letters were sorted into bundles and labelled by Field and his daughter, and this arrangement has been kept. In addition, there is a journal kept by his father John Bousquet Field as a midshipman in 1839; his own journal, 1870 to 1871; a diary from 1881; and some personal reminiscences, undated. Other items comprise ephemera and printed material. There is also a memoir by his friend Commander George Keith Gordon of the Navy's attempts to suppress the slave trade off east Africa in 1873. The National Maritime Museum also holds some charts by Field relating to his surveying voyages and those produced under his aegis as Hydrographer.

Administrative / biographical background
Arthur Mostyn Field entered the Navy as a cadet in 1868. He recieved the Beaufort Testimonial in 1875 after gaining the highest score in navigation and pilotage in examinations for the rank of lieutenant. After a few months on HMS BLACK PRINCE, he embarked on his career in surveying and hydrography, the branch of the service in which he remained. From 1876 to 1880 he served on the surveying vessel HMS FAWN and in 1881 was employed in his first piece of independent work, as Admiralty surveyor for the Oil Rivers in the Niger delta. From 1882 to 1884 he served on HMS SYLVIA and his first command was HMS DART in 1885, surveying around New Guinea and Tasmania. In 1889 he was promoted to commander and served from 1890 to 1894 on HMS EGERIA around Borneo. He was twice commended by the Admiralty for his surveying work. In 1895 he was promoted to captain and from 1896 to 1899 commanded HMS PENGUIN, surveying islands in the south west Pacific including deep borings on Funafuti atoll under the auspices of the Royal Society. This was his last foreign service and he spent the next four years surveying in home waters on HMS RESEARCH. In 1903, in company with HMS FLIRT, he was involved in sounding experiments at speed in the Channel with the resulting tables bearing his name. Field was Hydrographer from 1904 to 1909, was promoted to the rank of rear-admiral in 1906, and in 1909 was appointed the first Admiral representative on the Port of London Authority, a post he held until 1925. In 1910 he retired and the same year was promoted to vice-admiral on the retired list, becoming admiral in 1913. In 1905 he became a Fellow of the Royal Society and in 1911 received the KCB. From 1910 to 1930 he was Acting Conservator of the River Mersey, and was a Nautical Assessor to the House of Lords. As a leading authority, he wrote on surveying and revised and enlarged the "Hydrographical Surveying" of his predecessor as Hydrographer, Rear-Admiral Sir William Wharton, publishing the 3rd edition in 1909 and the fourth in 1920. With Purey-Cust he patented the Field/Cust automatic tide-recorder in 1908.