Nelson class secondary armament

Nelson and Rodney carried twelve 6" in twin turrets and six 4.7" AA, which they retained throughout the war. Raven and Roberts in British Battleships of World War II mention a late-30s proposal to rearm them with dual-purpose guns, although it did ot proceed. There were three concepts:

Twelve 5.25", six twin mounts, presumably in place of the 6", probably atop the original barbettes. Not a very powerful secondary, but very easy to install.

Two other options would require reconstruction of that part of the ships: sixteen 5.25" as in the King George V class or twenty 4.5" in BD (Between Decks) mountings as in reconstructed capital ships like Valiant or Renown.

Curiously they did not mention removal or replacement of the 4.7s, but it seems unlikely that the ships would retain duplicate AA batteries, especially so close in caliber. There might well have been additional pom-poms in the 4.7s' place.

Presumably the four 6" directors would be replaced by High Angle Control Systems.

As it was, the ships had a single HACS on a tower atop the bridge structure, just abaft and overlooking the main armament director, a typical position for a high-angle director. R&R note that Nelson was fitted with a second HACS early in the war. For the longest time I could not spot this on any plan or photo of the ship. My first thought was that it might be aft, another common arrangement, plus in this case two of the AA guns were on the quarterdeck - but no. Some ships had two HACS side by side, but no, several photos clearly show a single unit on the centerline. Finally I spotted the second HACS, on a platform immediately abaft and below the first; that is to say they were located together on the forward superstructure but oriented so they both have a clear field of view aft - an odd-looking arrangement but in keeping with the layout of the ships and guns. Of course once I knew where it was, it was perfectly obvious on some of those same photos.