Keith Willshaw wrote:

The Atlas remains in production to this day in the form of the II,III
and V but the design has been continually updated since the
60's and the Atlas now has the highly efficient Russian designed
RD-180 engine.

The Atlas V is not a pressure-supported structure - it has an isogrid
tank structure that does not require pressure to support itself. The
II and III essentially use the same pressure-supported tankage as
before, lengthened and adapted as necessary.