WWII Blood Chits and Silk Evasion Maps

A downed airman behind enemy lines needed two things a rifle could not give him: a way to ask a stranger for help across a language barrier, and a way to know where he was. Blood chits and silk maps were the paper-thin answers to those problems, and both survive today as some of the most collected artifacts of the air war.

These objects belong together because they belonged together in the field. Aircrew flying over occupied or hostile territory carried an evasion kit, and a printed appeal for aid and a concealable map were usually part of it. This page treats each as a documented category: what a blood chit is and how the reward system was meant to work, how silk escape and evasion maps were produced and why silk was chosen, and the two intelligence organizations that designed and distributed this material. The photographic record of the air war sits on the military photograph archive, and the wider treatment of wartime images and aircrew subjects is covered under WWII photography and wartime historical images.

What a blood chit is

A blood chit is a notice carried by a service member, usually an airman, that identifies the bearer as an ally and asks whoever finds him to help him to safety, generally with the promise of a reward paid by his government. The text is printed in the languages of the region the bearer might come down in, so that a farmer or fisherman who reads none of the others might read one. The tradition is older than aviation. It is commonly traced to 1793, when the French balloonist Jean-Pierre Blanchard flew in the United States carrying a letter of introduction addressed to citizens who would not share his language. The object answers a specific problem: an isolated flier cannot negotiate, so the appeal has to speak for him.

The best-known wartime example came from China and belonged to the Flying Tigers. General Claire Chennault's American Volunteer Group flew P-40 fighters for China against Japan from 1941, months before the United States formally entered the war, and its civilian American pilots carried a chit printed with Chinese text asking soldiers and civilians alike to rescue, shelter, and give medical aid to the foreign airman who had come to help, often alongside a Nationalist Chinese flag. Many were worn on the back of the flight jacket where a rescuer could read them at a glance. When the United States entered the war, the practice was formalized and extended across every theater, with chits printed in the many languages an evading crewman might need.

Silk escape and evasion maps

An evading airman also needed geography, and an ordinary paper map failed him in several ways at once. It rustled, it tore, it turned to pulp in rain or seawater, and it would not fold small enough to hide. The British answer came from MI9, the branch of military intelligence formed in December 1939 to support escape and evasion. Its escape-aids work is associated above all with Christopher Clayton Hutton, the officer who set out to print maps on a material that solved every one of those failures.

Silk did. A silk map opened in silence, survived immersion, and folded into a space no larger than a matchbox, which meant it could be sewn into a lining or hidden in a boot heel. The Edinburgh mapmaking firm of John Bartholomew and Son waived its royalties so the underlying maps could be used freely. The technical obstacle was ink, which bled and blurred on woven silk until Hutton and the printers found that adding pectin thickened it enough to hold a clean line. As silk grew scarce the same maps were run on rayon and on tough tissue paper, so the category is more accurately escape and evasion maps on cloth and specialty paper than silk alone. The maps were also printed by Waddington, the maker of the board game Monopoly, which helped conceal them inside game sets sent to prisoners of war through cover organizations.

MI9 and MIS-X: the organizations behind the objects

The American counterpart to MI9 was MIS-X, the Military Intelligence Service branch established in October 1942 and run from Fort Hunt in Virginia under the cover designation P.O. Box 1142. MIS-X assembled the escape and evasion kits issued to aircrew, trained personnel in evasion, and ran a concealment program of remarkable ingenuity. Escape aids were hidden inside hollowed shoe brushes and game boards, maps were laced into playing cards that separated into sections, and compasses were disguised as ordinary buttons and pencil clips. Much of the paper record was deliberately destroyed after the war, which is one reason the surviving physical objects carry so much of the documentary weight today.

Clandestine and survival field gear as a category

Blood chits and maps were the printed end of a broader field of escape, evasion, and survival equipment, and collectors treat that whole field as one category. It includes the miniature escape compass, from swinging-needle button types to luminous studs; purses of local currency and gold sewn into kits for bribery and passage; concealed hacksaw blades and files; aircrew survival tins holding fishing line, matches, and water-purifying tablets; and the optical and signaling instruments a downed crewman used to fix a position or attract a rescuer. These items were made to be hidden, which is exactly what makes them hard to authenticate. A genuine button compass and a postwar novelty can look identical in a photograph, so identification turns on construction detail, materials, and any documented issue markings rather than on appearance alone.

Identifying evasion material

Across blood chits, maps, and concealed aids, authentication follows the same discipline used elsewhere in this archive. Read the object before the story attached to it: the printing method and how ink sits in the weave of a cloth map, the languages and exact wording of a chit, the sheet or code numbers a genuine map series carries, and the construction of a concealment device. Weigh how easily each feature could be faked, and give the most weight to the features hardest to reproduce, such as period printing registration and honest material aging. Museum holdings make comparison possible. The Imperial War Museum, the National Air and Space Museum, and the collection interpreting Fort Hunt document escape and evasion material against which a piece in hand can be checked. Because so much of this equipment was made in quantity and has been reproduced for decoration and reenactment ever since, provenance matters more here than in almost any other militaria category. The problem of chain of custody is treated at length in the reference on historical military artifacts and personal effects. The archive home page explains how this archive is arranged and why it states identification methods rather than unverifiable specifics; that note sits on the archive home page.