Lots of coated originals for the KM, LW & WM available here: http://www.binoculars-cinecollectors.co ... k_p_4.html
As for the effect of the lens coatings, they really can't be understated (esp. in large complex optical equipment) as with the Zeiss hard coatings the light transmission was improved by over 80% pr. lens, and since most optical equipment used 4 or more lenses (large naval equipment used far more) this added up in the end. This is esp. true with the German use of multicoating, i.e. the coating of all lens surfaces.
![Image](http://www.meade.com/support/images/bincoat.gif)
But you are right that there are other ways to combat this problem, one is simply to use a lower amount of lenses, but this limits you in other areas, such as magnification & FoV. Another method is by using bigger objective & occular lenses, something the Germans were already doing on top of using coatings, and the Japanese started doing the same in the 1920's.
This is probably also the reason why German & Japanese rangefinders featured so much higher a magnification performance, 50x on the German RF's, and 30x on the Japanese RF's on the Yamato. You needed better glass and/or coatings to achieve this whilst still maintaining an acceptable brightness of image.
Also regarding the Japanese optics, their optics industry was created with help of German advisors and technological support starting in 1917, and many new technologies were traded during WW2, incl. the use of Lanthanum as well as H (Helligkeit) glass. Some more information here:
http://www.referenceforbusiness.com/his ... ATION.html
Thus it is no surprise that Japanese optical equipment impressed the US, they were basically looking at German equipment, albeit uncoated.
PS: I remember reading that prior to the war the British admiralty was very concerned regarding the RN's inferior optical equipment in comparison to regular uncoated Zeiss binoculars. So much so that a competition was arranged with various British optics companies to come up with an equal piece of equipment. IIRC Barr & Stroud came closest, but with a much larger piece of equipment.