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John Penn & Sons of Greenwich were marine engineers.
1799/1801 John Penn, Senior began in business on his own account at Greenwich, where he soon became known as a millwright, especially for flour mills, where he made many improvements particularly in the substitution of metal for wood framing. Penn devised heating systems for the conservatories of his wealthier neighbours, and won a small contract for the supply of biscuit baking apparatus to the Royal Victualling Yard at Deptford.
c.1818 The treadmill for prisons, designed by William Cubitt in 1818, was first executed at Mr. Penn’s works.
Benjamin Cubitt was foreman of the works of Mr. Penn at Greenwich.
1825 Marine engineering started at Greenwich.
1833 Began to make marine engines with oscillating cylinders, first fitted to paddle-boats which plied between London and Richmond.
1830s John Penn gradually took on the management of the whole works.
1838-42 See 1839-1842 Marine Engine Makers for details of engines made for the Admiralty
1843 John Penn, Senior died.
1843 John Penn approached the Admiralty with an offer to install high-power oscillating engines in the Admiralty steam yacht Black Eagle. The success of these engines led to Penn's installing further examples in many of the last paddle-wheel warships through to 1852.
1843 Commissioned to make oscillating engines for the Phoenix of 260 h.p., and in 1844 for the royal yacht tender.
For naval screw-propeller vessels Penn developed the trunk engine, which combined horizontal cylinders for safety below the waterline with the highest power yet achieved.
1845, October, Penns were commissioned to supply direct-acting trunk engines, for the Arrogant and Encounter, each of 360 nominal h.p.
1848 Engine from wreck of SS Xantho on display at Western Australian Maritime Museum. The engine was one of a batch built for naval vessels in the Crimean War. It was subsequently fitted to a small merchant vessel, SS Xantho, owned by Charles Edward Broadhurst, which sank in 1872. It was recovered in 1985 and preserved following extensive archaeological investigation. An interesting aspect of the work was that when corroded bolts were removed and had to be replaced to hold the engine together, the screw threads of many of the fasteners were in good condition, and modern British Standard Whitworth nuts purchased locally 'off the shelf' could be used. An early example of the benefits of standardisation. By coincidence, Broadhurst married the sister of Joseph Whitworth.
John Penn and Sons was considered the best-equipped marine engineering works. The works grew in size in response to the naval demand as well as to meet the orders for mercantile and liners.
1851 Award at the 1851 Great Exhibition. See details at 1851 Great Exhibition: Reports of the Juries: Class V.
1852 Refitted SS Great Britain with oscillating engines of 500 h.p. which gave the vessel substantial capacity for speed.
1856 Subscribed £100 to the Smith Testimonial Fund, commemorating the work of F. P. Smith in promoting the screw propeller.
1861 Engine for HMS Warrior. Description in The Engineer of May 1888)
1871 John Browning constructed the first wind tunnel, located in Greenwich at Penn's Marine Engineering Works. It had been designed by a fellow member of the Aeronautical Society, Francis Herbert Wenham.
1872 John Penn took his two elder sons into partnership, and retired from the more active duties of the business.
1875 John Penn retired from the firm. Company employed more than 2,000 men.
1878 By the time of John Penn's death, the works occupied 7 acres on Blackheath Hill, and there was a separate boiler works at Deptford. By this time the company had fitted 735 vessels with engines. John's son, John Penn (1848-1903) was chairman.
1881 Employing 970 men and boys 
1896 Engine for PS Victoria for Cosens and Co of Weymouth
1896 Engine for PS Consul for Cosens and Co of Weymouth
1898 Horizontal Engine with gear drive for Metropolitan Water Board (West Wickham Station)
1899 The Thames Iron Works, Shipbuilding and Engineering Co was registered on 15 July, to take over the business of the Thames Iron Works and Ship Building Co, with which was amalgamated the undertaking of John Penn and Sons. 
1914 The company closed.