Hello Ron - and a very warm welcome to the forums !
That's a very interesting and worthwhile project you're doing....
I've only had a little time to go back to my books, but here's what I can come up with so far ( plus a little guesswork ).
Firstly, the places in Essex ( BTW, ''over here" we always just refer to the name, we never say 'Essex County'
) :-
Great Dunmow, Earls Colne and Andrewsfield were actual airfields, Braintree is a nearby medium-sized town and Marks Hall a smaller village. The last two almost certainly would have housed USAAF administrative units.
All three airfields in early 1943 were operating B-26 Marauders under 8th AF control ( Dunmow : 386th BG, Earls Colne : 323rd BG, Andrewsfield : 322nd BG ). Although all three airfields and units were passed to 9th AF during October 1943, on the very date you mention ( July 17th, 1943 ) the 322nd resumed operations from Andrewsfield following a lengthy period of intensive training for medium-level formation attacks.
After transfer to the 9th, these Groups were heavily involved in pre-D-Day precision bombing, as well as post-D-Day attacks on German forces. I've taken the above info from various works by Roger A Freeman and Michael JF Bowyer.
Personally, I think that any research in this area is very worthwhile. The wonderful efforts of the B-17 Groups have really taken the spotlight away from the activities of the B-26 Marauder units ; very little firm information is available.