Under Congleton’s arrangements, as many ships as possible had been brought into the Clyde and Forth at the last moment; and thereafter the Navy blocked the entrances with mine-fields upon an enormous scale. Nothing, either surface craft or submarine, could have penetrated either estuary. Aerial defence was a secondary matter. No invasion in force would come by that road; and the destruction of the aerodromes had disposed of any early attempts at mere malicious damage. Defences were established, however, around the central area; and to accommodate the aeroplanes and airships which had been brought North, immense flying-grounds were laid out on the level reaches of the lower Clyde. The storage of the food-supplies cost much thought; but by utilising every spare corner, including railway and tramway depots, it had been possible to get them all under cover and under guard. A strict rationing system was put in force, though the allowance was quite up to normal quantities. The main trouble was, as Nordenholt had anticipated, a shortage of vegetables; and there was also a considerable deficit in the meat-supply. However, after a complete census had been taken, it seemed likely that we should be able to hold out without much difficulty. These material factors had given little trouble in our arrangements; but when the human counters came into the question, the resulting complications were much greater than appeared at first sight. Taking the problem at its simplest, we had coal at the one end and manufactured nitrogenous products at the other; and the quantity of the latter depended roughly on the amount of the former, since coal represented our source of energy and also part of our raw material in certain of the processes employed. But, in addition, we needed coal for lighting, either by gas or electricity, and also for heating; so that our actual coal output had to be larger than that required for the mere fixation of nitrogen. Then the number of miners had to be adjusted in proportion to those of the remaining workmen in each stage of the process; for it was wasteful to feed men who were employed in producing a superfluity which could not be utilised. Again, the problem was complicated by the fact that the coal could not immediately be used as it was hewn. Time had to be allowed for the construction and erection of the machinery whereby the atmospheric nitrogen was to be fixed; and this introduced further complications into the calculations. Finally, to omit intermediate details, the number of labourers required for spreading the nitrogenous manure upon the soil was governed by the quantities of this material which could be prepared.