Tracy White wrote:
I view early as until about April 1944 and late as from about October/December 1944. April '44 was when Essex had what was essentially the first major overhaul and change and we start seeing the extra quad 40mms sprouting. Yorktown, Bunker Hill, Franklin, and Ticonderoga were overhauled in short order starting in October 1944 and came out with a lot of similar alterations, and in between those periods was sort of a mish mash (Intrepid, for example, had the extra three starboard quads added under the island but retained the single quad on the stern whereas the others got the three and the double quad 40mm installation on the stern at the same time [note, from memory and I might be wrong - still at work so no time to look at notes for an hour or two]).
This is entirely my categorization though. Others may have one that makes more sense or logical breakdown.
Here's my slightly different categorization (;)): Lex had the first repair/refit after her torpedo damage off Kwajalein. During her repair/refit is when she got the 3 outboard 40mm quads below her island and the two quad 40mm mounts starboard aft, which all the mid-1944 carriers got. IMO, she kind of lead the way of adding additional highly visible/distinguishable 40mm quads. I am really surprised she didn't get the bigger flag bridge at this time, which Essex got just a few months later. (I'd love to know why!)
Essex got the first flag bridge retrofit to see action (Intrepid might have slightly beat her to completion, but she didn't see action until mid-summer '44). But Essex only got a few (four, IIRC) additional 40mm mounts, and the starboard aft weren't even moved outboard during the war. It's not like she had to go through the ditch again. Maybe a difference between the two could be explained by the shipyards that repaired them: PSNY for Lex and Hunters Point for Essex (IIRC without going to reources).
I agree that starting with Yorktown in the late summer of '44, she became the pattern for the "ultimate" configuration that combat experience determined for the rest of the other "single-40mm-bow-mount ships" (CV-13, CV-17, CV-11, CV-16, CV-18, CV-12, etc.) that followed.
(I'm tired and I hope that makes some sense... Off to bed!)