Over the course of the war, the OSRD explored thousands of possible research projects, selecting the ones with the greatest
potential tactical advantage. At the beginning of the war, scientists were asked to focus on primary military needs: weaponry,
transportation, and medical equipment. As the war continued, many of the initial research problems were solved and scientists
were transferred to new projects. By 1944, the U.S. military began to focus on projects that, while not as significant as
bomber planes or missiles, would give the Allied forces the advantage needed to finish the work in Asia, Africa, and Europe.
Invisible ink was one of these projects.
The military application of invisible inks was established by the beginning of the early twentieth century and was expanded
upon during World War I. Unfortunately, many of the inks and developers were limited in their usefulness by a variety of
physical and chemical characteristics. Oftentimes, the invisible inks left visual traces like ghost images, discolored water
spots, and bleaching which could be used to identify documents containing secret writing. Even worse, most inks used in the
early twentieth century could be made visible with a wide range of common developers including but not limited to household
acids like vinegar, other dying processes, and even the application of biological substances like blood and urine. This meant
that invisible writing was rarely secure.
Beginning in mid-1944, the OSRD assigned the invisible ink project to Arthur Lamb, a scientist at Harvard who had developed
inks for the military during the First World War. Lamb suggested that the project be expanded to include other researchers
and, in September 1944, Linus Pauling became an official investigator in the OSRD's Invisible Inks project.