Originally Posted by
Alan Baker
The 707 fuselage lower lobe was deeper than the forward fuselage lower lobe of the 727 (thus the double bubble effect was less noticeable on the 727). The rear fuselage of the 727 was deeper than the forward section (a feature perpetuated on the 757). The 737 used the 727's forward fuselage section throughout its length. The C-135 was not circular, it just didn't have a crease line, which reappeared when the 707 upper lobe was widened for 6 abreast seating.
Thankyou Alan. This makes everything much clearer.