[Milsurplus] Speaking-Tube system in Japanese aircraft

[Hue Miller]

Saw in a 1943 Japanese book "Front 8-9" a photo from rear 
of observer in a 2-place Japanese plane. Nearby photo shows
a view of a single engine plane with fixed faired landing gear,
is this "Babs" ? Don't have my recognition manual handy. Anyway
observer is wearing a headphone with a cord that caught my attention,
looks like about the size of hardline coax. Enters left headphone 
element right at center. Another such cord disappears to front of pilot
unseen. At first i puzzled over the size of these cords, then realized
that this was a "speaking tube" system. I know this was "once" used
in US planes but certainly not into WW2. Now this puzzles me too: 
the plane has an antenna mast. Why did they not just use the audio
section of the radio for the intercom? Of course, there is no guarantee
the photo of the plane with the antenna is the very same plane as the
observer photo. I have never heard of anyone in USA owning such a 
WW2 Japanese headset.  This book has interesting photos of Japanese
airfields, in - i assume - the Aleutian Islands, Alaska. I will need to copy
and post these somewhere. Not quite sure how to scan them as book
is very oversized. -Hue Miller