Fourth (or sixth?) son of Sir Edward Mansel (died 1585), of Penrice, Oxwich, and Margam, by his wife, lady Jane Somerset, daughter of Henry, 2nd earl of Worcester. His career, which is described in the D.N.B., touches the naval history of England much more closely than it did Wales but it is of interest to recall that, by the marriage of his nephew, Sir Lewis Mansel, there was a family connection with the Gamage s (of Coity, Glamorganshire), and hence with lord Howard, lord admiral, with whom, it is said, Mansel first went to sea. He served in the Cadiz expedition and was knighted, 1596, and had a long career in the navy, of which be became treasurer in 1604. He was imprisoned in the Marshalsea prison in 1613 for alleged political disaffection; in 1618, however, he became vice-admiral of England and in 1620-21 he was engaged in expeditions against Algiers.
Mansell's activities as treasurer of the Navy, his close connection with his countrymen, Sir John Trevor, surveyor of the Navy, and Sir Thomas Button, and with Phineas Pett, master shipwright, are discussed in the following publications of the Navy Records Society : (i) Two Discourses of the Navy: The Navy Ript and Ransact, 1659, by John Hollond, and A Discourse of the Navy, by Sir Robert Slyngesbie (ed. Tanner, 1896), (ii) The Autobiography of Phineas Pett (ed. Perrin, 1918), (iii) The Naval Tracts of Sir William Monson (ed. Oppenheim, 5 vols., 1902-1914). It may be added that these contemporary naval papers suggest that Mansell's appointment as vice-admiral in 1618 was not in fact a promotion, but rather a deliberate removal to a less influential position because of his dishonest administration from 1604 to 1618. The charges brought against him seem to have been well founded, but he remained secure in the favour of the king despite his inglorious expedition to Algiers in 1621.
He was M.P. for King's Lynn in 1601, for Carmarthen in 1603, Carmarthenshire in 1614, Glamorgan in 1623 and 1625, Lostwithiel in 1626, and again for Glamorgan, 1627-8.
From 1615 Sir Robert had been interested in the manufacture of glass, a share in the monopoly of which he had secured in that year. There is a brief reference to this matter of glass-manufacture in the D.N.B., but much fuller detail is given by C. A. Maunsell and E. P. Statham in History of the Family of Maunsell (Mansell, Mansel), i, chap. xii. From a statement made by Sir Robert in defence of his patent during the debate in the Commons on the Monopoly Bill in 1624 it would appear that he endeavoured to establish factories in various places - London, the Isle of Purbeck, Milford Haven, and the Trent Valley. John Brand (Hist. of Newcastle) says - ' We may venture to fix the beginning of the glass-works upon the Tyne about 1619, where they were established by Sir Robert Mansell. … The cheapness of sea-coal was no doubt his chief inducement for erecting them at so great a distance from London.'
The reference to sea-coal is significant. As Sir Robert's process involved the use of sea-coal instead of wood the monopoly was to some extent of the nature of a legitimate patent, but it was constantly necessary for him to defend it against those who wished to infringe the patent and against those who attacked monopolies; for details see Maunsell and Statham, op. cit., where also is reproduced the title (in facsimile) and the text of A True Report of the Service done vpon Certaine Gallies passing through the Narrow Seas; Written to the Lord high Admirall of England, by Sir Robert Mansel Knight, Admirall of her Maiesties forces in that place (London, 1602).
Sir Robert, who died in 1656 (his will was administered by his widow on 20 June 1656), had been twice married: (1), before 1600, to Elizabeth, daughter of Sir Nicholas Bacon, lord keeper, and (2), 1617, to Anne, daughter of Sir John Roper. There was no issue of either marriage.
Published date: 1959
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