Kriegsmarine vs IJN?

[Kazuaki Shimazaki II]

Originally Posted by the_tyrant

who would win?
assume war started 1945 between germany and japan
both navies have everything that they ever built
EDIT: germany took south africa and japan took Singapore
only consider navies, in total naval war

Though this is a pretty dumb scenario, I'll go on a limb and say the Germans actually have a strategic edge here.

On the surface, the Japanese have a much superior Navy. However, even at their peak they never developed real power projection. So, though they'll basically experience next to no direct resistance when bombing (since the Kriegsmarine technically has no air arm at all, and the scenario says "only consider navies"), they can only bomb a few times before they have to run home to refuel. The practical limitations of Japan's oil supply even on its best day likely means they don't have that many runs in them.

The sum of the damage it can do to Germany is, even if not purely tactical, merely operational. Even if the IJN wipes out every German ship and sub, ultimately Germany is a land power. In a peacetime environment, it'll resupply by land. Even if the Japanese manage to mount some kind of blockade despite the distance, Germany would only be inconvenienced for a good long time.

Now, let's look at the Germans. Their surface fleet will basically be a goner, true, but it has a lot of subs. If you let them have everything they ever built, there will be something like a thousand of them, including almost 300 long range IXs and even a few XXI (and as many as over 100 if you assume all the wartime production bottlenecks that kept a lot of them from putting out to sea wouldn't appear in this peacetime-start scenario). In either case, such a force would be a critical problem even for the Allies (for all their ASW prowess and tech, the real Allies fought those thousand submarines a few score at a time as they were built and brought into action over the years), and the Japanese were relatively weak at ASW.

If you hit the Japanese merchantmen supply lines with these one thousand subs AT ONCE, or in waves of hundreds so you can maintain a continuous presence, the Japanese lines of communications would be shut down in short order, thus creating a strategic crisis in Japan. You can use some of the shorter range subs to flood the area in front of your naval bases or block off choke points and make it a truly risky business for the Japanese carrier force to come close enough to bomb.

Short version is, if you count only navies, ironically only Germany has a force structure (coupled with Japan's geography) that gives it a chance of a "strategic" win that would bring Japan to its knees and amenable to negotiations from which substantial, strategic concessions can be extracted.