- The Grant webpage had an interesting question about headquarter flags.
Rosecrans issued orders pertaining to their use in his army which are
"Flags will be used to indicate the various headquarters, as follows:
General headquarters-the National flag, 6 feet by 5, with a golden
eagle below the stars, 2 feet from tip to tip. Right wing-a plain
light crimson flag. Center-a plain light blue flag. Left wing-a plain
pink flag. First Division, right wing-the flag of the wing, with one
white star, 18 inches in diameter, the inner point 1 inch form the
staff. Third Division, right wing-the flag of the wing, with three
white stars, each 18 inches in diameter, set in triangular form, the
outside star 1 inch from the outer line of flag. The division flags of
the center and left wing will correspond with the above; that is to
say, they will be the flags of the center of left wing, as the case
may be, and with one, two, or three white stars, each 18 inches in
diameter, according as they represent the First, Second, or Third
Divisions. The headquarters flags of all brigades will be the flags of
their divisions, with the number of the brigade in black, 8 inches
long, in the center of each star. That of the brigade of regulars,
however, will, instead of the white star and black number, have simply
a golden star. The flags of the wings will be 6 feet on staff by 4
feet fly; those of the divisions and brigades 5 feet by 3. They will
all be of a pattern to be furnished to the quartermaster's department.
Artillery reserve-a plain red flag, equilateral in shape, each side
being 5 feet. Cavalry reserve-of the same shape as division flags, 3
feet fly by 5 on the staff, but of deep orange color. Divisions and
brigades to be designated as in the infantry; that is, the First,
Second, and Third Division by one, two, and three white start
respectively; the First, Second, and Third Brigades by black figures
in each star. Engineer corps-a white and blue flag, blue uppermost and
running horizontally. Flag 5 feet on staff by 3 feet fly. ospitals and
ambulance depots-a light yellow flag, 3 feet square, for the hospitals
and for the principal ambulance depot on a field of battle; 2 feet
square for the lesser ones. Subsistence depots or store-hourse-a plain
light green flag, 3 feet square. Quartermaster's depots or
store-houses-same flag, with the letters Q.M.D. in white, 1 foot long."
He later found that this wasn't sufficient to distinguish the various
HQs, and submitted further instructions. Hurlbut also issued detailed
orders on flags and corps badges.
Such standardization would seem to have made the finding and
identification of HQs easier for the army's aides and messengers,
especially during battle or periods of movement.