The WW2 information I DO have, are the ONI recognition manuals that were aboard US submarines for... IDing and targeting shipping.
The information is very sketchy, and they admit it. They rate the information quality A, B or C for each ship. Many are "C." Of the As, only a tiny fraction have any rpm information at all.
The japanese didn't mass produce shipping like the US Liberty and Victory types, so any rpm data gotten would apply to only a couple ships. The only way to get the data is to count the turns, and accurately get the speed by another method. At that point you can write it down, and when you RTB it can be published (the rec manuals were looseleaf for easy addition/removal of pages). I have the 44/45 revised edition. There is squat for RPM data. Maybe 15% have 1 rpm at 1 speed listed.
Once surface radar was common, that was how the range was determined quickly. with accurate range and bearing, speed---actual speed, not a rpm guestimate---falls out.
tater
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