The collection was compiled by purchase between 1931 and 1939 and consists of nine early seventeenth-century manuscript volumes. These include 'A Treatise of Sea Causes, containing a yearly observation of English and Spanish fleets that were set forth one to annoy the other, from the year 1585...until the year 1602', 1624, by Sir William Monson (1569-1643) (printed by the Navy Records Society, ed. N. Oppenheim, 2 vols, 1902); 'Observations and overtures for a sea fight upon our coasts', with orders and directions to be given by an Admiral and rules for the men on board the ships, ca.1607; instructions issued by the Earl of Nottingham (1536-1624), ca.1607, and by the Duke of Buckingham (1592-1628), ca.1618, for the government of the Navy; a copy of 'The Sovereignty of the Seas of England', ca.1615, by Sir John Borough (d.1643); a copy of 'The Seaman's Dictionary', ca.1623, by Sir Henry Mainwaring (1587-1653), (printed by the Navy Records Society, ed. G.E. Mainwaring and W.G. Perrin, 1921); the reports of the Commissioners appointed in 1618 to remedy abuses in the Navy and to examine the accounts, ca.1618; instructions issued by the Earl of Northumberland (1602-1668) for the management of fleets under his command in 1636 and 1637, with journals of the voyages, May to October 1636 and April to September 1637; and 'A Brief Discourse of the Navy', 1638, by John Hollond (fl.1624-1659), (printed by the Navy Records Society, ed. J.R. Tanner, 1896).

Administrative / biographical background
The volumes in this collection were part of the collection of the tenth Earl of Northumberland (1602-1668), who was Lord High Admiral between 1641 and 1642. At his death the property, which included these volumes, passed from his daughter into the Somerset family and in 1750 was inherited by a cousin, Lord Egremont. On Egremont's death in 1837 the property passed to George Wyndham, a cousin, who in 1859 was created Baron Leconfield.