I came across this reference to them in the Preston Guardian (21st April 1900) "Mr. Adalbert Hay, the American Consul at Pretoria, confirms the report that the members of the Chicago Ambulance Corps have taken up arms for the Boers instead of remaining with the hospital, as they pledged themselves to do before they left America."
Many of them returned to the US later that year; in the New York Times of 16th November 1900 -
TRANSVAAL SOLDIERS HERE.; American Scouts and Irish Cavalrymen and Chicago Ambulance Corps Men on Two Liners.
Six American scouts and forty-four Irish cavalrymen of the Boer army arrived in this country on the Hamburg-American liner Furst Bismarck last night. The Americans return because, they say, their citizenship has not been renounced, while the Irishmen intimate that their coming was due to the fact that since Ireland is "nominally" British territory, their welcome in that country might not be as enthusiastic as they should wish.
(full article not accessible)
More information here
archiver.rootsweb.ancestry.com/th/read/I...O/2008-01/1201332134
including mention of some casualties -
Edward Eagan of Chicago, killed at Thaba 'nchu, Michael O'Hara of Holyoke, Massachusetts, killed at Watervalonder; John J. Reilly of Chicago, wounded at Thaba'Nchu and sent to St Helena. Prisoners: Michael Hearn and John Dougherty of Holyoke, Massachusetts, and Joseph Hill of Chicago....all sent to Ceylon.
As I'll be in Chicago next month I'll see if I can find the time to look up the issues of the Chicago Times that are mentioned and get copies of the articles.
The San Francisco Call of 12th February 1900 reported "IRISH AMBULANCE CORPS FOR THE BOERS. CHICAGO, Feb. 11. - The ambulance corps, thirty-nine in number, recruited and equipped by the United Irish societies of Chicago, left for New York to-day on its journey to join the Boer army on the battlefields in South Africa. On arriving at Pretoria the men will join the Boer army and work under the flag of the American Red Cross Society."
The same newspaper, in its 12th April 1900 edition, reported "AMBULANCE CORPS DELAYED ON SUSPICION. LONDON, April 12. - The correspondent of the Daily Mail at Lourenzo Marques, telegraphing on Wednesday, says: The departure of the Chicago ambulance corps for Pretoria was delayed on suspicion of filibustering. The members left by special train this afternoon, accompanied by a motley following of French and Germans, 100 in all. The departure only occurred after many stormy interviews with the Portuguese authorities. The members have no passports and no credentials beyond a letter from Miss Clara Barton to the effect that she knows some of them personally and believes them to be genuine, but many have openly expressed their intention of fighting. The Boers are paying from £30 to £40 per month for such recruits." "
(Clara Barton was president of the American Red Cross)