AJFFM -- You asked:
Obviously PoWs were released on successive groups, when was the first major group of PoWs were released?
Here's a brief chronology, with references, for releases in the US Zone:
15 May 1945 -- Supreme Headquarters gave authority to discharge certain categories of prisoners of war and members of the disarmed enemy forces. Those to be discharged first were all men of German nationality who were agricultural workers, coal miners, transport workers, and other urgently needed workers provided that they lived in the area in which they were imprisoned and were not war criminals, security suspects, or members of the SS. All women members of the German armed forces were also to be promptly discharged, provided that they lived in the area in which they were imprisoned and were not war criminals, security suspects, or members of the SS. (
US Army Occupation Forces in Europe 1945-46, part 5, p. 132).
18 May 1945 – Supreme Headquarters gave authority to discharge all prisoners of war over fifty years of age, provided that they lived in the area in which they were imprisoned and were not war criminals, security suspects, or members of the SS. (
US Army Occupation Forces in Europe 1945-46, part 5, pp. 132-33).
5 Jun 1945 – Nationals of France, Belgium, the Netherlands, and Luxembourg who were prisoners of war or in the status of disarmed enemy forces and not wanted for war crimes by a country other than their own were released to their respective governments. (
US Army Occupation Forces in Europe 1945-46, part 5, p. 133).
30 Jun -- General discharge was authorized for all Germans except war criminals, security suspects, the large number in automatic arrest categories, and those whose homes were in the Soviet zone. Of these exceptions, the last were held pending an agreement with the Soviet Union on their transfer; the others were discharged on condition that they be held as civilian internees for trial or other disposition. (
US Army Occupation of Germany 1945-53, p. 90).
Jul 1945 -- authority was given to release to their governments all non-Germans who were not security suspects or wanted as war criminals by a country other than their own, with the exception of Estonians, Latvians, Lithuanians, and Poles not claiming Soviet citizenship, and dissident Yugoslav and neutral nationals with ardent Axis sympathies. (
US Army Occupation Forces in Europe 1945-46, part 5, p. 133).
mid-August 1945 -- 732,000 POW's and 588,000 disarmed Germans were held by US armed forces in Germany.
Both received the POW ration. (
US Army in WWII - The Quartermaster Corps; operations in the war against Germany, p. 534).
Sept 1945 – Rheinwiesenlager camps closed. (
http://en.wikipedia.org/wiki/Rheinwiesenlager)
Oct 1945 -- Prisoners of war and disarmed enemy forces of all services in the custody of the United States in October numbered 1,474,074. Of these, 3,243 were in the Bremen enclave, 157,000 in Italy, 609,948 in Theater Service Forces, 355,351 in the Zone of Interior, and the remainder -- 348,532 -- in the United States zone of Germany. (
US Army Occupation Forces in Europe 1945-46: Disarmament and Disbandment of the German Armed Forces, pp. 45-46).
Nov 1945 -- The US had 1,007,807 prisoners in custody in Europe in Nov 1945 – 81,823 in hospitals, 400,615 in camps and 525,369 in work programs. (
US Army Occupation Forces in Europe 1945-46: Disarmament and Disbandment of the German Armed Forces, p. 32).
15 Jul 1946 – US held 206,657 POWs in Europe. (
US Army Occupation of Germany 1945-53, p. 90).
viewtopic.php?p=1667004#p1667004There is a chronology of the captures of German POWs in western Europe a little further up on the pages of that thread, at
viewtopic.php?p=1666714#p1666714