This could refer to:
Joseph Cotterill, born 1918, the son of John and Margaret Cotterill. He married of Annie Elizabeth.
Joseph served in the Royal Navy aboard HMS Orion with the rank of Ordinary Signalman. His service number was P/JX 222998. Joseph died on 25ty September 1941 aged 23 and is commemorated on the Portsmouth Naval Memorial Panel 52, Column 2.
Joseph William Cotterill born in Brecknockshire in 1915.
Joseph served in the Royal Engineers, 606 Railway Construction Company with the rank of Lance Serjeant. His service number was 2073585. Joseph died on the 9th July1945 aged 30 and is buried at Rangoon War Cemetery 3. F. 20.
The connection of either man with Penarth is unknown.