Any unit in the free game C-evo can be integrated into the resource cost of a new unit being produced in the same city - but contributing only two-thirds of its original resource cost, multiplied by the current health of the unit (rounding down fractions). "Z" is the quick key. Take care not to integrate a transporter that is carrying any units: those units will be lost; integrate or unload them first. In each case, any surplus above what is needed to finish the unit or building is likely to be lost.