Please create a new life story:
#386136 B Coy Private in 1/1 Northumbrian Field Amb, RAMC (CWG In mem cert)
CWGC War Dead: https://www.cwgc.org/find-war-dead/casualty/331298/thoburn,-harry/ , inc certificate, location, Death registration
POW at Worms, (Hochheim Hill) May - Sept 1918 (Brit Red Cross records)
grandeguerre.icrc.org_en_File_Print_E_04_01_C_G1_E_04_0 (listed erroneously as Thobwin)
Images of cemetery
plus service record confirms match :-)
He has a page here https://livesofthefirstworldwar.org/lifestory/4398098 under his early Territorial number. RAMC territorials are really difficult to research as the RAMC only put 1 number on the cards (the number held when first serving abroad) and so if the man served overseas with a 4 digit number but died after 1917 with a 6 digit number it's often hard to make the connection. In this case however the card does state that he died on the date shown by the CWGC and it's an uncommon name.