During the Franco Prussian war, Parisians used hot air balloons to deploy flocks of homing pigeons out of their city to countryside and vice versa. With the advent of micro photography in the 19th century pigeons could carry as many as 30,000 messages by a single bird.
It wasn’t until 1942 the Army finally authorized an organic veterinary detachment for all the pigeon units deployed overseas. Each unit of a veterinary Corps had an officer who was either first Lieut. or Capt. and then one enlisted technician. A company unit was divided into three combat platoons each with 1500 pigeons. By organizing the birds in this way the Army was able to determine the necessary medicines and medical instruments to maintain every unit.