IIRC, the tubing on the frame is stainless steel, thus the "Submariner" name. Not sure if it's all stanless or just the main three tubes.
Cool looking frame, but heavy. I know cause I used to compare these Kabuki Submariners bikes to other bikes weightwise in the 80's by lifting them off the bike shop floor and was surprised that they were so heavy. I was hoping the SS tubing meant lighter weight but it didn't. The SS tubing was more for long life/corrosion resistance as you can see from the example in the pic from the OP.

Chombi