The pigeon post was in operation while Paris was besieged during the Franco-Prussian War of 1870-1871. The normal channels of communication into and out of Paris were interrupted during the four and a half months of the siege, and it was not until the middle of February 1871 that the Prussians relaxed their control of the postal and telegraph service. For an assured communication into Paris, the only successful method was by the time-honored carrier pigeon. Thousands of messages, official and private, were thus taken into and out of the besieged city.

On September 2nd, 1870 it was suggested that all pigeons in Paris should be sent away to be ready to bring messages back into Paris, and that pigeons should be brought into Paris from the North of France to be ready to carry messages out of Paris. During the course of the siege, pigeons were regularly taken out of Paris by balloon. Initially, the pigeons carried by a balloon were released as soon as it landed so that Paris could be apprised of its safe passage above the Prussian lines. The pigeons were taken to their base after their arrival from Paris and when they had been fed and rested, they were ready for the return journey. Before release, they were loaded with their dispatches. The first pigeons each carried a single dispatch, which was tightly rolled and tied with a thread, and then attached to a tail feather of the pigeon. The dispatch was protected by being inserted in the quill of a goose or crow, and it was the quill which was then attached to the tail feather.

Initially, the messages were written out by hand in small characters on very thin paper, but Charles Barreswil, a chemist of Tours, proposed the application of photographic methods with prints of a much reduced size and of which an unlimited number of copies could be taken. The prints were on photographic paper and varied in size, not exceeding 40mm to permit insertion in the quill. The officer directly charged with the pigeon service was De Lafollye, an amateur photographer. He was assisted by Gabriel Blaise, who was a professional photographer of Tours. This service flourished and De Lafollye was extremely proud of its success.

At the Exposition Universelle of 1867 in Paris, the photographer Rene Dagron, had demonstrated a remarkable standard of microphotography, which he had described in "Traite de Photographie Microscopique". He now proposed to Post Master General Germaine Rampont-Lechin that his process should be applied to pigeon messages. Minister of Finance, Ernest Picard, declared Mssr. Dagron the "chef de service des correspondances postales photomicroscopiques". Arrangements were made for him to leave Paris by balloon, accompanied by colleagues, Albert Fernique; professor of engineering , Jean Poisot; artist and son-in-law of Dagron , Gnocchi; Dagron's assistant, and Pagano; the pilot. They departed on November 12th in the appropriately named balloons Niepce and Daguerre, but the latter, with the equipment and pigeons in it, was shot down and fell within the Prussian lines and lost. The Niepce was also shot down and landed in Prussian-held territory. Dagron and his companions just escaped capture, losing their equipment and becoming separated. It was Fernique who first reached Tours on November 18th followed by Dagron on November 21st. Dagron and his companions were to serve under De Lafollye, using Dagron's superior technique. He had sought to reproduce a page of the Moniteur in 1 sq mm; to do so required laboratory equipment and processes that were unobtainable in Tours. On December 15th, he was able to start work in earnest. Thereafter, all the dispatches were on microfilm with a reduction of more than 40 diameters. These microfilms weighed about 0.05 gm. and a pigeon would carry up to 20 of them. Whilst Blaise's messages contained a page of letter press in about 37 by 23mm, Dagron put the same information in about 11 by 6 mm, a better than three-fold improvement in lineal measure. The pigeon dispatch service was put into operation for the transmission of information from the Delegation to Paris and was opened to the public in early November. The introduction of the Dagron microfilms eased any problems there might have been in claims for transport since their volumetric requirements were very small. When the pigeon reached its particular loft in Paris, the microfilm was carefully unpacked and placed between two thin sheets of glass. The photographs were then projected by magic lantern on to a screen where the enlargement could be easily read and written down by a team of clerks. The transcribed messages were written out on forms and so delivered. Many who were involved in the pigeon post had done a valuable service to France. The pigeon fanciers, aeronauts, veterans, Mssr. Dagron and his colleagues could sum up what they had done with satisfaction. The total of all the messages they had handled, including the copies, had reached almost one hundred and fifty thousand including perhaps a million private letters and dispatches - as many words as would be contained in a library of five hundred books.