The first coal was raised in 1902,[1] with the workings connected underground to the Universal Colliery in Senghenydd for ventilation purposes.
On 1 June 1902, a platform collapsed in the mine, tipping nine men into 25 feet of water, which had gathered in the sump.
Three managed to escape drowning by clinging onto floating debris, but the other six lost their lives.
[1] As a result, the colliery was taken over in the early 1930s by Powell Duffryn Steam Coal Company.
Production was later concentrated at Nantgarw, with Windsor kept open for ventilation, methane extraction and an emergency way out.