Hi Krakatoa,
With the 4.5", one per side may be good, two must be better.
With respect, I think in this instance that may not be the case - you'll note that on US battleships, for instance, the 5" DP mounts - which can be quite close to each other horizontally - are given vertical separation to prevent the barrels clashing. On your design, if the forward 4.5" develops a fault (or takes combat damage) that prevents traversal of the mount while it's pointed out to the broadside you pretty much lose the forward arc for the aft gun.
My suggestion would be to make a decision - if it's something the must work at any cost, set the mounts superfiring. One end will be a little worse than it is now and the other end will work better. If it's not, why the extra weight? Anything big enough or tough enough to require a barrage from two 4.5", you can just shoot with the 15" instead...
Regards,
Adam
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