370 F. H. Todd 
In that part of his paper which compares the two types of tanker on the basis of the 
same deadweight, Dr. Todd assumes, from data provided by other authors, a ratio of dead- 
weight to displacement in a nuclear propelled submarine of 0.6 (see Fig. 8). With this 
value of 0.6 the DHP curves of the circular sectioned submarine tanker in Figs. 9, 10, and 
11 lie below those of the surface tanker at all speeds worth considering. The crossover 
points beyond which the submarine tanker has the advantage over the surface tanker are 
11, 14, and 22 knots for equal deadweights of 18,750, 56,250, and 93,750 tons respectively. 
This paints a rather rosy picture for the submarine, but if the ratio of deadweight to dis- 
placement for the submarine tanker is less than 0.6, a very different picture would be 
obtained. It is not clear from the paper how the authors concerned arrived at their figures 
for this ratio, but it is significant to remark that the values indicated in Fig. 8 show a much 
wider scatter than those for surface tankers. Immediately I notice that Dr. Van Manen gave 
in his paper a figure of 0.41 for a 100,000-ton tanker and 0.50 for a 43,000-ton tanker. There 
is only one way to arrive at a realistic figure, viz., by carrying out a detailed design, and, 
speaking with some experience in the design of military submarines, I venture to suggest 
that a more realistic figure would be nearer to 0.5 than 0.6, for several reasons. The most 
important of these is the inherently unsuitable shape of the pressure hull to accommodate 
machinery and equipment with a degree of compactness consistent with good maintenance 
such as is possible in a surface ship. Others include the weight and space necessary for 
additional ship services such as trimming and compensating systems, special air-condition- 
ing apparatus, three sets of control gear (two hydroplane gears and one rudder gear), addi- 
tional navigational and operational aids, and the fact that many of the ship services must 
be designed to much greater pressures than in the case of a surface ship. The effect of a 
lower deadweight/displacement ratio would be to raise the submarine curves in Figs. 9, 10, 
and 11 and to greatly increase the speeds at which the submarine gains the advantage over 
the surface tanker to such values as to raise grave doubts as to whether the machinery to 
drive the vessel at such speeds could be accommodated. In the case of the 56,250-ton 
tanker in Fig. 10, for instance, if a deadweight/displacement ratio of 0.5 were used the 
crossover point would rise to the region of 27 knots and the DHP required to 118,000. 
Immediately the question arises “could the machinery and propellers to provide this 
power be accommodated in any reasonable size of pressure hull to suit other requirements?” 
I am strongly of the opinion that it could not. If this opinion is correct, it follows that, if 
for any reason a submerged tanker of such size became necessary, then with the presentmeans ~ 
of propulsion and types of fuel it would be necessary to accept a very heavy loss in dead- 
weight ratio compared with a surface tanker. 
Against this, however, must be weighed the distinct advantage of being able to 
operate with impunity in any weather except when approaching the terminal points of the 
voyage, as pointed out by Dr. Todd. 
In the section of the paper dealing with operating problems, Dr. Todd has called 
briefly, but very effectively, to the need to take account of dynamic stability and control 
when submerged. Even with the comparatively small military submarines now being built, 
the problems involved are both complex and numerous. Compared with the submarines of 
the last war, underwater speeds have doubled and trebled. The speed beyond which the 
submerged tanker begins to gain over the surface ship is in this region. Consequently the 
time available to the commanding officer, and to whatever control apparatus with which the 
submarine is equipped, to take corrective action is very much shorter —not more than one- 
third of that in an orthodox submarine of the last war. 
Fortunately much has been learned regarding the dynamic stability and control of 
normal sized submarines. By the application of theory and model experiments correlated to 
