Our own Gary,
@centaur567, can attest that the Environmental Control System (ECS) was a God Send in the 'Nam weather. This was retrofitted to many Cobras in the field. This explains why Gary stated that the canopies should have a blue tinge (clear canopies being used on new builds in the latter part of '68). Supposedly, going to clear as the tint interfered with night vision and the ECS took care of the shading effect for which the tint was applied.
OKAY, now what? Well, the pre-ECS Cobras had different ducting and this was visible behind the pilot.
Pre-ECS:
ECS for those built with it or retrofitted (5 and 18 are visible but the latter doesn't need changing):
In this photo of AH-1G 68-15197, Viva Santana, we see the blue canopy tinge, the duct behind Charles, and...
that the ECS was retrofitted in the field:
It is retrofitted here as well:
No ECS:
Here is where it gets confusing, AH-1G 69-16437 was built with the ECS (clear canopy is a clue) but has the vent connection at the extreme starboard side even after conversion to AH-1S!
Even more interesting is that she has, as Bettie K, the early ceramic gunner's seat with the armor between the ears!
Clearer in this earlier photo:
So what? SO WHAT?
SO WHAT?
I have yet to see the rear wall as the kits all provide. All the 'Nam era Cobras that I chose will need to have that rear wall reworked!
These are the best set of photos (from another Cobra which was upgraded to AH-1S and then back-dated to G):