Did the Joint Chiefs have personal flags when the positions were held (respectively) by Marshall, Eisenhower, Bradley, King, Nimitz, and Arnold? If so, what did they look like? (pics would be appreciated if available)
As far as I know, they didn’t have a personal flag. There are flags for their ranks.
According to the US Army Institute of Heraldry, the flag for the US Army Chief of Staff was approved in 1917, with the Vice Chief’s flag approved in December 1949.
The flag for the Chairman of the Joint Chiefs of Staff was also approved in December 1949.
The Army Institute of Heraldry website does not appear to indicate when the flags of the other service chiefs came into service. I’m not sure exactly when those officers served as service chiefs, so I’m not certain what positional flags they would have used when they served.