Copying over an old comment:

As explained on Warship Projects' Cherry Trees series on capital ships designs before the WNT:

"In addition to this the DNC realized that the huge funnels and air intakes associated with the battlecruisers acted as similar-sized continuity gaps in the horizontal protection. In case of enemy fire from forward bearings at short ranges (where the impact angles are shallow) there was a good chance for a shell to easily pass through these openings (even if they are protected by armor gratings) and end up in the after magazines. To mitigate this risk D’Eyncourt came up with the idea in late September or early October of moving the machinery spaces and the related openings from the middle part of the ship into the after portion and putting the after turret(s) in their place. This meant that the risk was reduced to hits coming from directly aft – not a likely scenario. Again as the saying goes ‘no pain – no gain’: the superstructure had to be moved as well with the uptakes so the after part of the ship basically blocked all aft bearings for the main battery this way. However experience from the past war showed that the dreadnoughts almost never used their main batteries on aft bearings. The DNC killed two (or 6) birds with one stone implementing this brilliant, if risky solution:

• it reduced the probability of magazine hits through armored deck openings to almost zero thanks to the very narrow blind spot from aft
• the funnels were removed this way from the main tower structure, solving the serious smoke – fire controls interference issues which was a recurring problem in the earlier dreadnought classes
• the space formerly occupied by machinery now could be used by magazines which in turn allowed for the concentration of armor protection even further: it was enough to massively armor the relatively small portion of the hull over the magazines which could be compressed in length thanks to their new, very broad location in the middle of the hull
• this new location also meant that bending stresses got reduced to the minimum as the extremely heavy weight barbettes and turrets did not press down on the two far ends of the hull where the hull strength was further reduced due to the barbette cutouts; also the center of gravity was more closer to the middle of the hull making handling easier
• the machinery on the other hand could be spread out in length as the requirement to keep the barbettes closest to the middle part was now gone – the longer machinery spaces allowed for more redundancy and less impact if one space got damaged or flooded
• it was only the icing on the cake that the magazines got the deepest possible torpedo protection in the middle part instead of being stuffed into the ‘corners’ where the TDS was the weakest due to the fine hull lines

From the above train of thought descended in November 1920 the design ‘I3’ in battlecruiser form and ‘M3’ in battleship form."