In collaboration with the architect Richard Norman Shaw, he built Cragside in Northumberland, the first house in the world to be lit by hydroelectricity.

In 1887, in Queen Victoria's golden jubilee year, he was raised to the peerage as Baron Armstrong of Cragside.

Armstrong married Margaret Ramshaw in 1835, and they built a house in Jesmond Dene, on the eastern edge of Newcastle.

Armstrong was a very keen angler, and while fishing on the River Dee at Dentdale in the Pennines, he saw a waterwheel in action, supplying power to a marble quarry.

When he returned to Newcastle, he designed a rotary engine powered by water, and this was built in the High Bridge works of his friend Henry Watson.

Armstrong subsequently developed a piston engine instead of a rotary one and decided that it might be suitable for driving a hydraulic crane.

Armstrong was involved in this scheme and he proposed to Newcastle Corporation that the excess water pressure in the lower part of town could be used to power a quayside crane specially adapted by himself.

Donkin, his legal colleague, supported him in his career move, providing financial backing for the new venture.

In 1847 the firm of W. G. Armstrong & Company bought 5.5 acres (22,000 m2) of land alongside the river at Elswick, near Newcastle, and began to build a factory there.

[2] In 1854, during the Crimean War, Armstrong read about the difficulties the British Army experienced in manoeuvring its heavy field guns.

He built a breech-loading gun[4] with a strong, rifled barrel made from wrought iron wrapped around a steel inner lining, designed to fire a shell rather than a ball.

Under his new position, Armstrong worked to bring the old Woolwich Arsenal up to date so that it could build guns designed at Elswick.

Armstrong was able to refute all of these claims in front of various government committees, but he found the constant criticism very wearying and depressing.

Also, because of a drop in demand, future orders for guns would be supplied from Woolwich, leaving Elswick without new business.

Compensation was eventually agreed with the government for the loss of business to the company, which went on legitimately to sell its products to foreign powers.

The ship was ill-fated, as she was involved in a collision with HMS Camperdown just six years later in 1893 and sank with the loss of 358 men, including Vice-Admiral Sir George Tryon.

An important customer of the Elswick yard was Japan, which took several cruisers, some of which defeated the Russian fleet at the Battle of Tsushima in 1905.

Notable among them were Andrew Noble and George Wightwick Rendel, whose design of gun-mountings and hydraulic control of gun-turrets were adopted worldwide.

In 1860 he paid local architect John Dobson to design a Banqueting Hall overlooking the Dene, which still survives, though it is now roofless.

In 1863 he bought some land in a steep-sided, narrow valley where the Debdon Burn flows towards the River Coquet near Rothbury.

Eventually the estate was 1,729 acres (7.00 km2) and had seven million trees planted, together with five artificial lakes and 31 miles (50 km) of carriage drives.

In 1869 he commissioned the celebrated architect Richard Norman Shaw to enlarge and improve the house, and this was done over a period of 15 years.

Armstrong entertained several eminent guests at Cragside, including the Shah of Persia, the King of Siam, the prime minister of China and the Prince and Princess of Wales.

His last great project, begun in 1894, was the purchase and restoration of the huge Bamburgh Castle[16] on the Northumberland coast, which remains in the hands of the Armstrong family.

[6] Such was Armstrong's fame as a gun-maker that he is thought to be a possible model for George Bernard Shaw's arms magnate in Major Barbara.

He also said: "It is our province, as engineers to make the forces of matter obedient to the will of man; those who use the means we supply must be responsible for their legitimate application.

In 1901 his heir, William Watson-Armstrong gave £100,000 (equivalent to £13,712,955 in 2023),[20] for the building of the new Royal Victoria Infirmary in Newcastle upon Tyne.