I can't see a Percy Reginald FIELDS born in 1901, so glywri is wrong about that.
There is this birth two years earlier
FIELDS, PERCY REGINALD mmn KILLY
GRO Reference: 1899 J Quarter in BIGGLESWADE Volume 03B Page 373
This corresponds with a birth on the MG Corps records of 26 May 1899
Regimental number 4679, Machine Gun Corps number 137819.
According to his records he served in France, Belgium and Russia
Father George FIELDS, Ivel Rd, Sandy, Beds.
Perhaps you have confused Belgium with the Balkans,