After basic ground instruction and then 'trade' training on the AT-11, cadets would then be sent to the relevant bomber (or transport) unit for continuation training on the type of aircraft they would fly/fly in, operationally, for example, B-17, B-24, B-25 etc.
This would again be a training unit, where the nucleus of a crew would form. On completion of this training, the crew, or possibly just individuals in some cases, would then be assigned to an operational unit, and posted to that unit's location.
If you have your Grandfather's Log Book, it should show the units, from training onward, even if this is only an endorsement stamp from the unit HQ, possibly on the last page of each qualification section, and/or at the front of the book. I'm not familiar with US Log Book format, compared to RAF, so I'm afraid I can't be more specific.