In fact many units remained segregated.
At the end of June 1950, the Korean War broke out. The U.S. Army had accomplished little desegregation in peacetime and sent the segregated Eighth Army to defend South Korea. Most black soldiers served in segregated support units in the rear. The remainder served in segregated combat units, most notably the 24th Infantry Regiment. The first months of the Korean War were some of the most disastrous in U.S. military history. The North Korean People's Army nearly drove the American-led United Nations forces off the Korean peninsula. Faced with staggering losses in white units, commanders on the ground began accepting black replacements, thus integrating their units. The practice occurred all over the Korean battle lines and proved that integrated combat units could perform under fire. The Army high command took notice. On July 26, 1951, the US Army formally announced its plans to desegregate, exactly three years after Truman issued Executive Order 9981.
Soon Army officials required Morning Reports (the daily report of strength accounting and unit activity required of every unit in the Army on active duty) of units in Korea to include the line "NEM XX OTHER EM XX TOTAL EM XX", where XX was the number of Negro and Other races, in the section on enlisted strength. The Form 20s for enlisted personnel recorded race. For example, the percentage of Black Enlisted Personnel in the 4th Signal Battalion was maintained at about 14 % from September 1951 to November 1952, mostly by clerks' selectively assigning replacements by race. Morning Report clerks of this battalion assumed that all units in Korea were doing the same. The Morning Reports were classified "RESTRICTED" in those years.
http://en.wikipedia.org/wiki/DesegregationI don't think back then they all went along so smoothly. Here's also an interesting tidbit about the Battle of the Bulge.
In the midst of the Battle of the Bulge in late 1944, General Dwight D. Eisenhower was severely short of replacement troops for existing military units--all of which were totally white in composition. Consequently, he made the decision to allow Afro-American soldiers to pick up a gun and join the white military units to fight in combat for the first time. This was the first step toward a desegregated United States military. Eisenhower's decision in this case was strongly opposed by his own army chief of staff, Lieutenent General Walter Bedell Smith. Indeed, it was stated that Bedell Smith was outraged by the decision and had said that the American public take offense at the integration of the military units.On edit a bit more:
Ironically, the most celebrated pronouncement on segregation at the moment of the Truman order came not from publicists or politicians but from the Army's new Chief of Staff, General Omar N. Bradley.7 Speaking to a group of instructors at Fort Knox, Kentucky, and unaware of the President's order and the presence of the press, Bradley declared that the Army would have to retain segregation as long as it was the national pattern. 8 This statement prompted questions at the President's next news conference, letters to the editor, and debate in the press.9 Bradley later explained that he had supported the Army's segregation policy because he was against making the Army an instrument of social change in areas of the country which still rejected integration.10 His comment, as amplified and broadcast by military analyst Hanson W. Baldwin, summarized the Army's position at the time of the Truman order. "It is extremely dangerous nonsense," Baldwin declared, "to try to make the Army other than one thing�a fighting machine." By emphasizing that the Army could not afford to differ greatly in customs, traditions, and prejudices from the general population, Baldwin explained, Bradley was only underscoring a major characteristic of any large organization of conscripts. Most import, Baldwin pointed out, the Chief of Staff considered an inflexible order for the immediate integration of all troops one of the surest ways to break down the morale of the Army and destroy its efficiency.11
But such arguments were under attack by the very civil rights groups the President was trying to court. "Are we to understand that the President's promise to end discrimination," one critic asked,
was made for some other purpose than to end discrimination in its worst form�segregation? General Bradley's statement, subsequent to the President's orders, would seem to indicate that the President either did not mean what he said or his orders were not being obeyed. We should like to point out that General Bradley's reported observation . . . was decidedly wide of the mark. Segregation is the legal pattern of only a few of our most backward states.... In view of the trends in law and social practice, it is high time that the Defense forces were not used as brakes on progress toward genuine democracy. 12
General Bradley apologized to the President for any confusion caused by his statement, and Truman publicly sloughed off the affair, but not before he stated to the press that his order specifically directed the integration of the armed forces.l3 It was obvious that the situation had developed into a standoff. Some of the President's most outspoken supporters would not let him forget his integration order, and the Army, as represented by its Chief of Staff, failed to realize that events were rapidly moving beyond the point where segregation could be considered a workable policy for an agency of the United States government.
The Army: Segregation on the Defensive
The President's order heralded a series of attacks on the Army's race policy. As further evidence of the powerful pressures for change, several state governors now challenged segregation in the National Guard. Generally the race policy of the reserve components echoed that of the Regular Army, in part because it seemed logical that state units, subject to federal service, conform to federal standards of performance and organization. Accordingly, in the wake of the publication of the Gillem Board Report, the Army's Director of Personnel and Administration recommended to the Committee on National Guard Policy14 that it amend its regulation on the employment of black troops to conform more closely with the new policy. Specifically, General Paul asked the committee to spell out the prohibition against integration of white and black troops below battalion level, warning that federal recognition would be denied any state unit organized in violation of this order. 15
http://www.history.army.mil/books/integration/IAF-13.htm