After four months in the trenches - a period
that strongly influenced the world that he later created in
books such as The Hobbit (1937) and The Lord
of Rings (1954-55) - Tolkien fell victim to the typhus-like
condition known as 'trench fever' and returned to England
in November. Unable to fully shake off its debilitating effects,
he spent the rest of war either in hospital or in home service
camps, where he did sufficiently well to earn promotion to
the rank of lieutenant.
The papers in Tolkien's service record file (WO 339/34423)
are largely concerned with the various health problems that
dominated his time in the army during the First World War.
There are numerous reports made by army medical boards between
December 1916 and September 1918 on Tolkien's recovery from
trench fever - a slow process punctuated by relapses.
The file also contains the document (dating from 22 November
1916) confirming his initial return to England from France
because of illness, and two short letters written by Tolkien
himself (in January and February 1917), in which he informs
Office that he is once again fit for duty.