Over the past couple of years The National Archives have been making all First World War unit war diaries available online, and have now got round to including medical units in France and Flanders. They are supplied as copies of original document and are not transcriptions, so some are not that easy to read. They vary in content but are simply a day to day account of the basic running of the units, so unlikely to supply much of use to anyone searching for individuals. A number of them give details of deaths in the form of name, number, unit and cause of death. Some of the diaries are rather good on detail for the early months of the war, but most fairly soon become simply a list of admissions, discharges and comings and goings of medical officers.
The reference to 'convalescent hospitals' should actually read 'convalescent camps' - the units in France where men were sent to recuperate if they were not so seriously ill or wounded that they needed to return to the United Kingdom. All these military hospitals are those that were run under the control of the War Office. They are in no way connected with any other auxiliary, convalescent or VAD hospital under the control of the British Red Cross Society and Order of St. John. Surviving records for those are very rare and if they exist are likely to be held in local or County archives in the UK.
With reference to the St. Louis Unit, they took over No.12 General Hospital, Rouen, from the British in the summer of 1917, and that war diary can be found under it's original British title and is available for download from TNA even for the period after the Americans took over.
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