[T]he heart of every base is the Construction Yard. On many occasions you will not start with this structure in place but will have an MCV, or Mobile Construction Vehicle, at your disposal. When deployed, this vehicle becomes a Construction Yard, providing you with all of the benefits of that building. To deploy an MCV, select the vehicle and hold the cursor over it. If the cursor changes to a golden circle with four arrows, left-clicking on it will deploy the vehicle. If the cursor has a red circle with a line through it, there is either not enough room to deploy or something is in the way. Move the vehicle (or the offending object) to find a suitable deployment site. - Command & Conquer: Red Alert 2 manual
Yuri's Revenge patch 1.001: a mind-controlled MCV can no longer be deployed, and a mind-controlled construction yard can no longer undeploy. This is done to bypass the issue of the MCV/construction yard from vanishing once the unit controlling it is killed. MCVs/construction yards controlled by psychic dominator are not affected.