TOP SECRET In making the final assessment of the possible use to the Russians of knowledge of progress in France, it is useful to consider what may be the limiting factors in the Russian programme. It is our considered opinion that the main limitations for the Russians will be the shortage of uranium, and difficulties connected with the engineering and construction of the large plants required for production of fissile material on a dangerous scale. In neither of these respects will knowledge of French progress, on what is little more than a laboratory scale, be of appreciable help.