[2] The sinking of the twin shafts in 1911 reached the coal seam at a depth of more than 850 yards (780 m) in 1915, placing them 2,000 feet (610 m) below sea level, making Nantgarw the deepest pit to be sunk in the South Wales Coalfield up to that time.
All the site's waste was dumped into the shafts to a level 60 ft below these new landings,[4] placed underground to keep the surface clear of unsightly spoil heaps.
The main heading was driven south, with the workings cutting through the No.1 Rhondda, Bute, Brass, and Hard seams due to the 36-degree dip to the north.
[6] The coke ovens and by-product plant were opened in 1951, as part of the NCB's modernisation of the regional and national coal industry.
[2] In 1982 output declined steeply as a major coal seam at Windsor became unworkable, while in 1984 an overtime ban led directly to the 1984/5 UK miners strike spreading to South Wales.