The Ship Model Forum

Let's say the Japanese Military Attache saw the German 80cm monster guns in progress and reported back, creating a stir back home. In a fit of barrel envy, the IJN works up an alternate weapon fit for the next superdreadnaught, So, the Musashi gets 80cm guns on enlarged turrets, 2 per, and the 15cm back ups are removed. To make up for that and to supplement the expected slow firing rate of the main guns, new long tube 15 or 21cm guns are fitted in broadside mounts. It is silly, but what to do with a half-slagged old Tamiya 1/350 now that the new kit is in hand? Fairly along in the work, made a resin copy of the new Yamato superstructure in order to give the super Musashi an original configuration bit and scratch-built a bunch of the details.
But wait, there's more!
I got crazy-lucky and got a partial sample of the new Yamato kit that Tamiya sent out as a teaser. Well, just the thing to build the alternate Shinano, the carrier battleship version. With it's generous beam and narrow superstructure, the hull allows for twin fly off decks flanking the superstructure with a wide aft flight deck. So, the IJN has both another superdreadnaught AND a carrier to supply it's own defensive fighter screen.
And, I'm doing a straight 1941 Yamato.
Once I figure out how to post images, I'll do just that.

Even a ship the size of the Yamato would have trouble with 80cm guns. (Roughly 31.5") You would have to settle for a twin turret forward and twin aft. Forget all of the 15cm guns. This Yamato would have lots of weight dedicated to the two large turrets. You would have four twin 12.7cm AA as secondary armament. No seaplanes as the weight will be needed for the guns. The gun barrels would need some form of support. The barrels might have to be kept verticle and dipped up to 15 degrees to fire. This monster would need heavy escort, such as 2 or 3 cruisers and twice that number of DD. Her value would be in land attack rather than anti-ship. It will be an odd looking build should be fun though.

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The design, as I've done it, has 35 calibre tubes, which are still pretty big, but not needing special support or anything like that. They will need to go to neutral for reload however. I've got 3.5m of recoil travel but expect only single barrels to be fired at a time. Right now I'm thinking of extra long tube 20cm guns for secondary armament. For the primary load on the 80s, I was thinking of saboted 46 cm AP and a thin case 80cm HE. Having a long range secondary set would help offset the need for escorts.
As for weight, yeah, the new 80cm turrets and barbettes would be heavy, but the removal of the centerline 15cm mounts entirely would help offset that. Replacing the two broadside 15s with six twin 20s would be a penalty, but the flak 12s don't have any range to compare with them.

Of course this is all an excersize in silly rather than a serious weapon system.

And just wait 'till you see the Yamato class battleship/carrier.