In WWII sites all over Alaska we find ingot iron (heavy corrugated iron)
bunkers made of curved sheets that bolted together into arched (or
sometimes fully circular) structures that were often buried. They were
manufactured by the ARMCO Company and have a stencil on their inside
surfaces which is usually still visible. Occasionally these were also
used for generators and similar purposes and they came in (at least) two
sizes- one about 8 feet in diameter and another about 25 feet in
diameter. I do not know whether ARMCO pre-dates WWII but I will try to
find out.

Catherine Williams
Northern Land Use Research, Inc.
Fairbanks, Alaska