US 8th and 9th Army Air Force in Gloucestershire

Hello everyone, 

I am wondering if anyone here may be able to help me with one of my many queries...

I have been trying to undertake research into the USAAF in Gloucestershire during the Second World War, so far I have found out that the US 8th and 9th Air Force were stationed in Gloucestershire during various periods during 1943 and 1944 as part of Operation Bolera and on the led up to D-Day. In 'Gloucestershire Airfields In The Second World War' written by David Berryman published in 2005, he mentions that the only USAAF units base in Gloucestershire during the war were Liaison Squadrons as well as "a massive Port In-Transit Depot was established nearby at Wapley Common...", he goes on to mention that the IX Base Aircraft Assembly Depot (BAAD) was based at Filton until early 1944. Later in his book he mentions that the USAAF briefly used Chedworth when the HQ Suadron of the 9th Air Force was based there between 19th June and 9th July 1944. 

I have access to the 14 editions of 'US Army / Army Air Force Units and Locations from Startion List Sorted by County' compiled by Philip C. Grinton ranging from 21.6.1943 to 16.12.1944. The first reference to the USAAF in Gloucestershire is on 31.12.1943 with the 8th Air Force In-Transit Depot Group, Port U 2, Det A being located in Wapley Common, Gloucestershire, subsequent editions have the following information:

21.2.1944
Wapley Common, Gloucestershire, 8 Air Force Int Depot Group, Port U 2 HQ Sqdrn, Det A.

31.3.1944
Wapley Common, Gloucestershire, 8 Air Force Intransit Depot Group
Filton, Gloucestershire, 9 Air Force Service Command, Detachment C

30.4.1944
Filton, Gloucestershire, 8 Air Force Intransit Depot Group, Detachment 102
Wapley Common, Gloucestershire, 8 Air Force Intransit Depot Group
Wapley Common, Gloucestershire, 8 Air Force Intransit Depot Group, HQ & HQ Det
Wapley Common, Gloucestershire 8 Air Force Intransit Depot Group, Detachment C
Wapley Common, Gloucestershire 8 Air Force Intransit Depot Group, Detachment E
Wapley Common, Gloucestershire 8 Air Force Intransit Depot Group, Detachment F
Wapley Common, Gloucestershire 8 Air Force Intransit Depot Group, Detachment I

31.5.1944 
Filton,Gloucestershire, 8 Air Force Instransit Depot Group, Detachment 102
Yate, Gloucestershire. 8 Air Force Instransit Depot Group, HQ & HQ Det

30.6.1944
Aston Down, Gloucestershire, 8 Air Force Intransit Depot Group, Detachment G
Aston Down, Gloucestershire, 8 Air Force Intransit Depot Group, Detachment G2
Filton, Gloucestershire, 8 Air Force Intransit Depot Group, Detachment H
Yate. Gloucestershire, 8 Air Force Intransit Depot Group, Detachment D

From the above research, I have the following questions and was wondering if anyone could possibly help me?

1. What is the role of the Intransit Depot Group while being station here?
2. What is the role of the 9 Air Force Service Command while being station here?
3. Was the IX Base Aircraft Assembly Depot (BAAD) an American unit?
4. What was the role of BAAD while being station here?

Sorry if some of these questions seem basic, I am relatively new to these aspects.

I would appreciate any help, guidance and/or assistance with regards the above. 

Thank you all in advance.

Aaron,
As you will appreciate, there was a huge buildup of US Forces camped in southern and south west England under the Bolero plan in support of Overlord.
I think many of your questions could be answered from the US Archive on-line known as Fold3:

www.fold3.com

This will require a subscription but opens up an incredible amount of information particularly under the group 'WW2 European Theater Army Records'
which can be accessed from the drop-down list under 'Browse' Bear in mind that the 8th and 9th USAAF were divisions of the US Army hence their history is intertwined with that force.