I recently came across a sketch of a Japanese battlecruiser design, labelled "B61". I instantly fell in love with the sleek looks and well balanced proportions, and now I have taken the time to try to bring her to life in SB form.
I had some misgivings initially, the mast looked odd and there is an error on the drawing: the guns are labelled as 14" even though the "3-Y" (presumably short for "3rd Year Type") is the designation for the 16.1" guns, and the turret dimensions fit the latter. I was however able to confirm the 4x2 16.1" arrangement via a specification sheet for this design in the Hiraga archives. The mast was apparently an early design evolution of what eventually became Nagato's 7-legged configuration, and I decided to retain it for its uniqueness.
The design itself is something of a missing evolutionary link between Nagato and the final Amagi cofiguration selected for consctruction. It is one of the battlecruiser variants in a series of "improved Nagato/Tosa" designs. The sketch itself is very bare bones regarding the superstructure, so I took the early drawings for the Amagi class as inspiration for the bridge and pagoda platform layout. This is a stylistic choice, along with retaining the very narrow hexapod mast, as I really like this look (and it gives variety). It is likely that had this ship (or Amagi for that matter) been built, the mast and bridge would have been upgraded during construction to more closely resemble the look of the Nagato class.
As the drawing evolved, it really came to life more than a simple design study, so I crammed in as much detail as I could muster and aimed for an "in-service" appearance in the mid-1920s, with aviation facilities inspired by those fitted to Nagato. To this end, I also came up with a name for the design, a mountain as per IJN practice for naming battlecruisers. Mount Sakurajima is Japan's most active volcano, befitting such a fiery ship.
Principal specifications on the sheet
Link to original sheet based on (as the image is large and widens the forum page too much):
https://i.imgur.com/obqVaXB.jpg
And the final drawing: