http://en.wikipedia.org/wiki/Kawanishi_H8K

Artist's commentary:
tittle:空中戦艦ムラサ
イベントでこのシリーズ出すたびに「二式大艇ないんですか？」と聞かれ、そのたびに「いやーもうネタとしては決まってるんですけど出るのは先になります」と答えてたんですが、つまりはこういう事です、はい。

もうね、二式飛行艇がどれだけ素晴らしい飛行機かってのはちょっとググれば幾らでも出てきますからね。日本が真に誇るべき最高の航空機だと思います。

ちなみに、スピナーの色と尾翼のマークは昔船の科学館にあった現物と同じにしてあります。

Artist's commentary:

Title: Flying Battleship Murasa
Every time I brought new pin-back buttons of this series to doujin events, I was asked if Kawasaki H8K was on sale. Then I replied "Well, I have an idea of it already, but I don't intend to release it just yet." Yeah, that was how it went.
What can I say? What a wonderful airplane the H8K is will become obvious if you just Google it a little! I believe this is the greatest airplane—one that Japan should truly be proud of.
For your information, I used the same color for the spinner and the same emblem on the vertical tail. in this image as those on the actual airplane that used to be displayed at the Museum of Maritime Science.

This flying boat—the only H8K in existence worldwide—was moved to the JMSDF Kanoya Air Base Museum in 2004.

Is this the flying boat shown in an early episode of You're Under Arrest?

Yes. Episode 1 of 1st Season / OVA.

The artist's tweet:

Here's a real interesting story. At this summer's Comiket, a member of the ShinMaywa Industries, a descendant of the Kawanishi Aircraft, bought my pin badge of H8K.