III Corps

The -300 was a bit longer than the -200 which was a stretch
of the original -100s which went to Lufthansa and then
PeoplExpress and eventually Continental. The -200 was
only slightly longer than the -100. Reportedly when
United got their first -200 and took off from ORD,
controllers said, "Nice punt!"

The -300 was also a slight stretch of the -200 with
as you noted, the CFM-56 engine. Likewise Boeing
elected to stretch again for the -400 for which PIEDMONT
was the launch customer. (PI and USAir both paid to
NOT have the upgraded cockpit for common training. ??)

The -500 was an airplane I never understood. It was
slightly longer than the -200 but with those big engines,
it was reportedly a little rocket ship. It just looked odd
with that short fuselage and big engines. (this one is
taking a long nap.)

Then Herb convinced Boeing to build him a 'baby 757'
which came with a new wing (faster, higher, longer range),
new engines, cockpit upgrades and more fuel for coast
to coast. BRILLIANT. Same type, many similar parts,
only differences training.

And now the -900.

More range that the Mighty Tri-Motor (727) but not as
fast and not as pretty.