They built numerous large research telescopes, including several that were (at the time of construction) the largest in the world of their type.

Leading up to and during the First World War (1914-18) the company produced periscopes for submarines and moved to St Albans in 1918.

[2] He ran a precision engineering company whose cast iron products included billiard tables and printing presses for banknotes.

[3] Grubb had a personal interest in optics and was a friend of the Irish astronomer Thomas Romney Robinson.

[3] His first foray into telescope construction was his own 9-inch (230 mm) refractor, which he operated as a public observatory in Portobello, Dublin, as a visitor attraction.

[2][3] Edward Joshua Cooper, the owner of Markree Castle, had purchased the optics from Robert-Aglaé Cauchoix of Paris and commissioned Grubb (on Robinson's recommendation) to construct the mechanical supports.

[3] This was followed in 1835 by a 15-inch (380 mm) reflecting telescope for Armagh Observatory (run by Robinson), which used the Cassegrain layout and another equatorial mount.

[5] In 1887 Grubb's firm built seven identical astrographs for the international Carte du Ciel project; the 13 inch refracting telescopes were designed to produce uniform photographic plates.

Howard Grubb, then in his 70s, attempted to revive the sale of large telescopes but the company began to lose money.

[4] Several telescopes had been delayed or not completed due to the war, such as a 24-inch (0.61 m) reflector for the National Astronomical Observatory of Chile (Santiago), which had been ordered in 1909, partially constructed in 1913, but was not operational until 1925.

[20] The next major project was the 98-inch (2.49 m) Isaac Newton Telescope for Royal Greenwich Observatory, which had moved to Herstmonceux Castle, completed in 1965.

The location was later deemed unsuitable, so from 1979-84 this telescope was moved to Roque de los Muchachos Observatory in the Canary Islands, during which Grubb Parsons upgraded it with a 100-inch (2.54 m) mirror.

[24] Ian Glass, a historian of astronomy, wrote a history of the company under the management of Thomas and Howard Grubb, based mostly on their letters.