​ ​The French navy being left unemployed during the minority of Louis XIV., Duquesne obtained leave to offer his services to the king of Sweden, who gave him a commission as vice-admiral in 1643. In this capacity he defeated the Danish fleet near Gothenburg and thus raised the siege of the city. The Danes returned to the struggle with increased forces under the command of King Christian in person, but they were again defeated—their admiral being killed and his ship taken. Peace having been concluded between Sweden and Denmark in 1645, Duquesne returned to France. The revolt at Bordeaux, supported as it was by material aid from Spain, gave him the opportunity of at once serving his country and gratifying his long-cherished hatred of the Spaniards. In 1650 he fitted out at his own expense a squadron with which he blockaded the mouth of the Gironde, and compelled the city to surrender. For this service he was promoted in rank, and received a gift of the castle and isle of Indre, near Nantes. Peace with Spain was concluded in 1659, and for some years afterwards Duquesne was occupied in endeavours to suppress piracy in the Mediterranean. On the revolt of Messina from Spain, he was sent to support the insurgents, and had to encounter the united fleets of Spain and Holland under the command of the celebrated Admiral de Ruyter. After several battles, in which the advantage was generally on the side of the French, a decisive engagement took place near Catania, on the 20th of April 1676, when the Dutch fleet was totally routed and de Ruyter mortally wounded. The greater part of the defeated fleet was afterwards burned in the harbour of Palermo, where it had taken refuge, and the French thus secured the undisputed command of the Mediterranean. For this important service Duquesne received a letter of thanks from Louis XIV., together with the title of marquis and the estate of Bouchet. His last achievements were the bombardment of Algiers (1682–1683), in order to effect the deliverance of the Christian captives, and the bombardment of Genoa in 1684. He retired from service in 1684, on the ground of age and ill-health. It is probable also that he foresaw the revocation of the edict of Nantes, which took place in the following year. He died in Paris on the 2nd of February 1688.

DUQUESNE, a borough of Allegheny county, Pennsylvania, U.S.A., on the Monongahela river, about 12 m. S.E. of Pittsburg. Pop. (1900) 9036, of whom 3451 were foreign-born; (1910 census) 15,727. It is served by the Pennsylvania railway. Its most prominent buildings are the Carnegie free library and club (opened in 1904 and containing 17,500 volumes in 1908), and the city hall. A short distance N. of the borough limits Kennywood Park, with a large auditorium and pavilion, is an attractive resort. By far the most important industry of the borough is the manufacture of steel. The value of the borough’s factory products increased from $20,333,476 in 1900 to $28,494,303 in 1905, or 40·1%. The municipality owns and operates its water-works. Duquesne was settled in 1885 and was incorporated in 1891.