James was born in Portsmouth on 25 February 1901, the third child to Nelson John and Bridget Elizabeth (née Fitzgerald, from Bantry Bay, Northern Ireland) Thompson. With his two brothers, Leonard (1896), Robert (1899) and sister Kathleen (1909), the family lived at 225, Twyford Avenue, Portsmouth.  In the Autumn of 1910 the father, Nelson, passed away and in 1915 Bridget married Harry J Harding and they had a child Daniel in 1915 while residing in 3, Wickham Place, Wickham Street. Portsmouth.

James entered the Royal Navy on 22 June 1916 at 15 years and 4 months of age when he entered the gates of HMS GANGES in Shotley, Suffolk, as a Boy Second Class on the basic training course. He qualified for Telegraphist training and was rated Boy Telegraphist on 25 November 1916. He completed his time in GANGES on 15 March 1917 with a draft to HMS DOLPHIN in Gosport for basic submariners training which he completed  on 4 June with a draft to HMS VULCAN operating out of ports in Northern Ireland.  On the 1 July 1917 he transferred to HMS H5  (on service docs H2) for operations in the Irish Sea.

On 2 March 1918, H5 was on surface transit when a merchant ship mistook her for a German U boat. SS RUTHERGLEN altered course and rammed the unknown submarine  which sank quickly with none of the 27 crew members managing to escape.

Boy Tel. 1c James Gerald Matthias Thompson aged 17 years and one week crossed the bar with all his crew mates. He is commemorated on the Portsmouth Naval Memorial on Panel 29.