Tim Barney wrote:

It was advanced for its time, being all-welded when most cars (even
of similar type) were
riveted construction.

As Bruce Smith observed, this comment about welding is way wrong.
The first extensively welded freight cars were covered hoppers in the
mid-1930s. Because of all the welding done during WW II, it was a
fully accepted construction method after the war. Freight cars,
certainly by 1950, were being extensively welded, INCLUDING flat cars
of several types (though maybe not so much on the PRR). Not to take
anything away from the "Queen Mary," which was quite a project--just
that welding isn't really part of its eminence.

Tony Thompson