Revisiting the Indiana Army Ammunition Plant

A few weeks back, I returned to the Indiana Army Ammunition Plant (IAAP), which was renowned for its production of smokeless gunpowder and other ordinances and, upon its completion, held the title of the world’s largest facility of its kind.

This government-owned, contractor-operated complex comprised three distinct facilities:

• Indiana Ordnance Works Plant 1 (IOW1), dedicated to smokeless powder production
• Hoosier Ordnance Plant (HOP), known colloquially as the “bag plant”
• Indiana Ordnance Works Plant 2 (IOW2), commonly referred to as the “rocket plant”

Construction of IOW1 commenced in August 1940 under the management of E.I. du Pont de Nemours & Co., employing a workforce of 27,520 individuals. It was finalized in May 1942, with a total expenditure of $74 million.

HOP’s construction began in January 1941, and by September of the same year, it was partially operational. The plant was fully completed in February 1942 for $27 million. It served as a facility for loading, assembling, and packing cannon, artillery, and mortar projectiles, featuring five distinct operational areas.

Construction of IOW2, designated for rocket propellant production, commenced in December 1944. While production commenced briefly, the plant remained unfinished following Japan’s surrender in August 1945, with construction halting on August 13th.

Overall, the Indiana Army Ammunition Plant spanned 19,200 acres and comprised 1,700 buildings, along with an extensive infrastructure including 84 miles of railroad track, 190 miles of road, and 30 miles of fencing. The total expenditure for its completion amounted to $133 million.

Enduring numerous encounters with ticks, enduring the intense heat and sunlight of spring, and occasionally spotting turkeys and deer, I embarked on a trek into INAAP alongside my friend Chelsea. For her, it marked her first visit—a journey she later proclaimed as her favorite exploration. And I understand why.

Our journey commenced near the initial stages of the ammunition manufacturing process. The Cotton Dry House served as our starting point, where cotton linters or wood pulp, delivered in rolls, underwent shredding. Subsequently, the material was pre-treated in large ovens to reduce its moisture content to less than 1% before being conveyed via ducts to the Nitrating House.

Next to the Cotton Dry House stood the Sulfuric Acid Concentration Plant, responsible for producing sulfuric acid through the melting and combustion of raw sulfur, resulting in sulfur dioxide gas. This gas underwent a process where it was directed over catalytic beds, leading to the generation of sulfur trioxide gas. Subsequently, the sulfur trioxide gas was absorbed into distilled water, producing sulfuric acid.

After the shredded cotton was blown in from the Cotton Dry House, it underwent a process where 32 pounds of cellulose fiber were mixed within stainless steel nitrators. These nitrators contained a blend of nitric and sulfuric acids. Following treatment, the acids were discharged from the bottom into centrifugal wringers, effectively removing most of the acid from the exterior of the wringer. The resulting wet nitrated cotton was submerged in water before the slurry was transferred to the Boiling Tub Houses.

The Blending and Wringer House played a vital role in the nitration process. It involved mixing portions of batches with varying nitrogen content to achieve a uniform propellant with consistent ballistic characteristics. In the Poaching House, slurry from the poaching tubs was conveyed onto vibrating screens for blending of nitrocellulose. The blended nitrocellulose then passed into collecting boxes, which were subsequently emptied into containers where guncotton and pyrocellulose were mixed.

Once the sample from the tub met the required nitrogen and solubility standards, the slurry was pumped into the Wringer House. Here, large volumes of water, used throughout the process to facilitate the movement of nitrocellulose, were removed. The containers containing partially dried nitrocellulose were then transported to the Dehydration/Press House via lag cars.

The poaching process served two main purposes: diminishing the acidity of the nitrocellulose and mechanically fragmenting the remaining fibers into minute pieces. Samples extracted from this process were dispatched to a nearby laboratory for analysis. There, experts determined the nitrogen percentage, the ether-alcohol mixture’s solubility, and the fineness degree.

The product was transported to the Mixer Houses, where it underwent mixing and kneading using a Baker-Perkins machine. Pristine and fully functional Bagged Toledo scales were utilized to weigh the powders accurately. Thick Goodyear-tired wooden carts were employed to transport the mixed product throughout the building.

The mixed product was then transferred to the Horizontal Press House. Here, single-based powder blocks underwent pressing through extruding dies to shape them into propellant.

The light gradually faded as the evening sun descended below the horizon. We decided to conclude our tour of IAAP earlier than originally planned. We exited the premises like we had entered: stealthily navigating through tall grass and brush, avoiding detection.