Several weeks ago, I revisited the Indiana Army Ammunition Plant. IAAP, which manufactured smokeless gunpowder and other ordinances, was the largest of its type in the world at the time of its completion.

The government-owned, contractor-operated plant included three separate facilities:

  • Indiana Ordnance Works Plant 1 (IOW1) that produced smokeless powder
  • Hoosier Ordnance Plant (HOP) that was referred to as the “bag plant”
  • Indiana Ordnance Works Plant 2 (IOW2) that was known as the “rocket plant”

Construction began on IOW1 in August 1940 under E.I. du Pont de Nemours & Co., employing 27,520 workers. IOW1 was finished in May 1942 at the cost of $74 million.

Work began on HOP in January 1941 and was partially in operation by September. Construction was completed in February 1942 at the cost of $27 million. The load, assembly, and pack facility was used to prepare cannon, artillery, and mortar projectiles and featured five distinct areas.

Development on IOW2, a rocket propellant plant, did not begin until December 1944. Although production did take place for approximately five weeks, the plant was never completed before the surrender of Japan in August 1945. Construction stopped on August 13.

In total, the Indiana Army Ammunition Plant contained 19,200 acres, 1,700 buildings, 84-miles of railroad track, 190 miles of road, and 30 miles of fence, and cost $133 million to complete.

Battling dozens of ticks, searing spring heat and sun, and the occasional turkey and deer sightings, I trekked into INAAP with my good friend Chelsea. For her, it was the inaugural visit – to which she later exclaimed that it was her favorite place to explore. I can see why.

We began from near the beginning of the ammunition manufacturing process. The Cotton Dry House was where cotton linters or wood pulp delivered in rolls, was shredded. It was then pre-treated in large ovens to reduce the moisture to less than 1% before being blown in ducts to the Nitrating House.

Adjacent to this was the Sulfuric Acid Concentration Plant that produced sulfuric acid by melting and burning raw sulfur, which produced sulfur dioxide gas. The gas was then passed over catalytic beds that generated sulfur trioxide gas, which was absorbed through distilled water that produced sulfuric acid.

With shredded cotton being blown in from the Cotton Dry House, 32 pounds of cellulose fiber were mixed in stainless steel nitrators that contained nitric and sulfuric acids that were blended. The treated acids were discharged from the bottom into centrifugal wringers that removed most of the acid through the exterior of the wringer. Wet nitrated cotton was immersed in water, and the slurry transferred to the Boiling Tub Houses.

The Blending and Wringer House was part of the nitration process. Portions of batches that had a high nitrogen content were mixed with others that had a low nitrogen content to obtain a uniform propellant and ballistic characteristic. Slurry from the poaching tubs in the Poaching House was fed onto vibrating screens where nitrocellulose was blended, which passed into collecting boxes. The boxes were then emptied into containers where guncotton and pyrocellulose were mixed.

If the sample from the tub had satisfactory nitrogen and solubility content, the slurry was pumped into the Wringer House. Large amounts of water that were used throughout the process to move the nitrocellulose was removed at the Wringer House. The containers of partially dry nitrocellulose were transported to the Dehydration/Press House via lag cars.

The poaching process was conducted to reduce the acidity of the nitrocellulose. It also cut the fibers remaining to minute fragments in a mechanical operation. Samples were sent to a nearby laboratory to determine the percentage of nitrogen, the solubility of the ether-alcohol mixture, and the fineness degree.

The product moved to the Mixer Houses where where it was mixed and kneaded by a Baker-Perkins machine. Bagged Toledo scales, in pristine and operable condition, weighed the powders. Wooden carts with thick Goodyear tires carted the mixed product throughout the building.

The mixed product moved to the Horizontal Press House, where single-based powder blocks were pressed through extruding dies to form propellant.

The light began to wane as the evening sun began to dip below the horizon. We decided to end our tour of IAAP earlier than expected and exited as we had entered: through tall grass and brush undetected.