A Mystery

I have received the following e-mail from Dan Gordon that contains a bit of a mystery….

I am a Londoner but have lived in Cardiff 50+ years.
My grandfather, James William Crouch, born Hampshire about 1880, was a deep sea diver who worked all around UK but spent some time working in Merthyr! He and my grandmother had two (of 13) children whilst there. He had a with a son of the same name who may have married in Merthyr but was killed World War 2.
What was a diver doing in Merthyr?
Can anyone shed any light on the above?