There’s not really anything left of the old Atlas in an Atlas V except the name “Atlas”. The Atlas 2 was the last of the family to retain elements of the original Atlas. The Atlas III went to the Russian RD-180 engines, and from that point on it’s pretty much just been a name.
The newer Atlases go something like this:
Atlas I—developed from the Atlas G, incorporating improvements from other “classic” Atlases and some improvements of its own.
Atlas II—Uprated MA-5 engine (MA-5A), stretched tanks. Old vernier engines replaced with new hydrazine models.
Atlas III-practically clean sheet design around RD-180s. Still uses balloon tanks, last vestige of classic Atlas in it. This model didn’t really draw any customers.
Atlas IV-there is no Atlas IV. Maybe there was one on paper at one point, but only the III and V saw daylight.
Atlas V-RD-180s with new tanks in a clusterable design. Nothing really left of the old Atlas but the nameplate.
Hmmn. Russian engines under a US “nameplate”, eh?
Thanks for the update.