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Day, Summers and Co of Southampton were shipbuilders and makers of steam engines for marine use.
Summers, Groves and Day was also established about this time
1837 they moved to Northam
1845 Partnership - Groves leaves. '...the Copartnership heretofore subsisting between us the undersigned, William Alltoft Summers, John Thomas Groves, and Charles Arthur Day, all of Milbrook, in the county of Southampton, and also of Northam, in the town and county of the town of Southampton, Engineers, Millwrights, Iron Founders, and General Dealers, carrying on business under the style or firm of Summers, Groves, and Day, was this day dissolved by mutual consent (so far only as respects the said John Thomas Groves)...'
Initially established a reputation as a builder of large mail steamers in the 1850s up to the 1870s when the North-east Coast and Clydeside yards took over that market.
1854 Partnership - Baldock leaves. '....the Partnership between the undersigned, William Alltoft Summers, Charles Arthur Day, and William Baldock, in the trades or businesses of Engineers, Millwrights, Ironfounders, and General Dealers, at Northam, in the parish of Saint Mary, in the town and county of the town of Southampton, and elsewhere, under the firm of Summers, Day, and Baldock, was this day dissolved by mutual consent, to take effect as on and from the 31st day of May last; and in future the said trades or businesses will be carried on by the said William Alltoft Summers and Charles Arthur Day, on their own joint account...'
At some point became C. A. Day and Co.
c.1868 Mr. Altoft Summers retired
1872 100-ton sheer legs for Chatham Dockyard
1870s The yard won orders from P and O for mail steamers, this was followed by similar orders from Royal Mail Line and then a series of re-engining orders. The yard then concentrated on building paddle steamers, coasters, yachts, Itchen floating chain bridges, Hythe ferries and sheerlegs.
1874 80-ton sheer legs for Aberdeen.
1880s The yard forged a good reputation for its steam yachts.
1882 150-ton sheer legs for the Russian Government
1889 Obituary of Thomas Summers in 'The Engineer'. 
1890 Engine for River Itchen Floating Bridge 'Vessel No 8' at Woolston.
1900s The company became of limited liability status. The yard continued making a variety of small ships: tugs, steam coasters and paddle steamers.
1905 Sheer legs for Chatham Dockyard. Tested with a load of 180 tons. Front legs 160 ft high. Back leg moved in and out by a leadscrew 11.5" diameter, 85 ft long, powered by its own steam engine.
1909 60-ton floating sheer legs for a South American customer.
1911 100-ton Sheer legs for Aberdeen. Powered by electrical equipment from J. J.(?) Holmes and Co of Newcastle. Delivered and tested within 5 months of date of order. This was the 89th set of sheer legs built by the firm, and the second for Aberdeen (see 1874 above).
1928 The yard continued with the above building programme until 1928 when it went into liquidation. It was taken over by Thornycroft.
1966 The yard became part of Vosper Thornycroft.
1987 The company ceased trading.