Jackpine Joe belongs to the 780th BS, 465th BG (55th BW) of the 15th AF. Their Squadron color was red, hence the call sign "red G".
 
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15th Air Force during WWII
Just a short note about the structure of the 15th Air Force (AF).
The 15th AF consists of five*) Bombardement Wings and two Fighter Wings (305, 306).
Its headquarter during the MTO time was situated in Foggia (South Italy). There are about 25 Bombardement Groups in the 15th AF. Jackpine Joe belongs to the 55th BW, 465th Bombardement Group with the corresponding airfield at Pantanella south of Foggia.
465th BG in the MTO
The 465 Bombardement Group (BG) is built of four Squadrons:
780th BS (red), 781th BS (yellow), 782 BS (white) and the 783 BS (blue).
Each bombardement group has its own unit identification which is usually painted on the rudder of the airplane. For example the 780th BG has a horizontal yellow bar in the lower half of the rudder.
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*) fifth BW?