Tom Clancy's Rainbow Six: Critical Hour is the fifth game in the Rainbow Six series, and was released March 14, 2006.
Critical Hour received a mixed reception due to its relatively small amount of content, although it was praised for following the roots of the first games, unlike Lockdown. Following poor sales its planned later release in Europe was canceled, as well as a port of the game for the PlayStation 2.
In Critical Hour, John Clark is retiring and passing the leadership of Team Rainbow on to Domingo "Ding" Chavez. He reminisces on the past missions of Team Rainbow. While cleaning out his office, he remembers seven missions from his years as the head of Team Rainbow. He leaves these missions for future members of Team Rainbow to study and to use for training.
Source: Wikipedia, "Tom Clancy's Rainbow Six: Critical Hour", available under the CC-BY-SA License.