The Tennis Court That Built the Bomb

In a quiet Dayton suburb, a private indoor tennis court became one of the strangest production facilities of the Manhattan Project.

During World War II, the U.S. Army and Monsanto converted Runnymede Playhouse in Oakwood, Ohio, into Unit IV of the Dayton Project — a secret plant built to isolate and purify polonium for the neutron initiators used in the first atomic bombs.

But Runnymede was only one piece of the operation. Laboratories, warehouses, former seminary buildings, and later the Mound facility formed a network spread across Dayton, largely hidden in plain sight.

In This Episode

Why the Manhattan Project needed polonium — and why Dayton became the place to produce it
How Bonebrake Theological Seminary became Unit III, the project’s main research and development laboratory
The transformation of Runnymede Playhouse from private tennis court to industrial polonium plant
The chemists, engineers, soldiers, and technicians who made the process work
How irradiated bismuth from Oak Ridge and later Hanford was turned into bomb-grade polonium
The health-physics problem of working with one of the most dangerous radioactive materials in existence
The mysterious “Dr. N.” and the worker whose urine samples revealed extraordinary polonium contamination
How Dayton’s polonium reached Los Alamos and became part of the initiators used in Trinity, Hiroshima, and Nagasaki
The dismantling of Unit IV, the cleanup of the Dayton sites, and what remains today

Today, Runnymede Playhouse is gone. Houses stand where the tennis court once held tanks, laboratories, and some of the most closely guarded chemistry of World War II.

But a few miles away, pieces of the Dayton Project are still standing — reminders that one of the most important parts of the atomic bomb was developed not in a remote desert, but in the middle of an ordinary Ohio city.

By the time the Army took over Runnymede in 1944, the old Talbott household was already gone. Katharine Talbott, who had built the Playhouse in 1927, died in 1935, and the family’s main residence on the estate burned in 1943. So the government was not displacing Katharine from an intact family home when it converted the property into Unit IV.

The family still controlled the Playhouse property through the Talbott estate and Talbott Realty Company, and the Talbotts themselves had not disappeared from Oakwood. Several members of the extended family continued living nearby in their own homes and estates along Runnymede Road and the surrounding neighborhood.

That helps explain why the property’s wartime takeover was less a story of a family being suddenly thrown out of its home and more one of the government acquiring a surviving piece of a once-larger family estate — a piece that just happened to contain an enormous indoor tennis court perfectly suited, at least from the Army’s point of view, for conversion into a secret chemical plant.

Unit IV — Runnymede Playhouse Site

Modern drive-by footage of Dixon and Runnymede, showing the exact neighborhood where the Playhouse stood. The video ends directly in front of the Playhouse / Site IV.

Dayton Project Warehouse — 601 E. Third Street

Modern footage of the surviving warehouse used for equipment, environmental monitoring, and worker bioassay. 601 E. Third Street is the brown building on the right, just after the white building with the mural.

A Map of Dayton Project Sites

A map showing the Dayton Project locations mentioned in this episode. I’ve made Runnymede yellow for easy identification.

An Overlay of the Runnymede Complex Over Modern Oakwood

See the full size overlay

Archival Images & Site Plans

The Dayton Project left behind a surprisingly rich visual record, including
site plans of Units III and IV, photographs of the surviving Unit III complex,
and images documenting the Manhattan Project facilities that supplied and used
the polonium produced in Dayton.

Surviving Manhattan Project-era building at the former Dayton Project Unit III site, 1601 W. First Street, Dayton, Ohio — **Surviving Unit III Building — 1601 W. First Street**
A clear modern view of one of the surviving Manhattan Project-era structures at the former Unit III complex in Dayton.Photo by Juliette Killen of Dayton/Vandalia.

Industrial side and service area of surviving buildings at the former Dayton Project Unit III site in Dayton, Ohio — **Unit III Service-Side View**
A closer view of the utilitarian side of the former Unit III complex, showing the industrial character of the surviving Manhattan Project-era buildings.Photo by Juliette Killen of Dayton/Vandalia.

Front and side view of a surviving Dayton Project Unit III building at 1601 W. First Street in Dayton, Ohio — **Unit III Surviving Building — Front and Side View**
A modern architectural view of one of the concrete-block buildings that remains from the Dayton Project’s Unit III laboratory complex.Photo by Juliette Killen of Dayton/Vandalia.

Surviving Unit III building viewed along the fence line at 1601 W. First Street, Dayton, Ohio — **Unit III Along the Fence Line**
One of the strongest present-day views of the former Unit III site, showing a surviving Manhattan Project building extending behind the perimeter fence.Photo by Juliette Killen of Dayton/Vandalia.

Detail view through the fence of a surviving Manhattan Project-era structure at Dayton Project Unit III — **Unit III Building Detail**
A closer look through the perimeter fence at the surviving fabric of the former Unit III complex.Photo by Juliette Killen of Dayton/Vandalia.

Fence-line perspective of the surviving Dayton Project Unit III complex in Dayton, Ohio — **Unit III Perimeter Perspective**
A long view along the perimeter of the former Unit III property, emphasizing the scale and continuity of the surviving wartime complex.Photo by Juliette Killen of Dayton/Vandalia.

Concrete foundation remnant at the former Dayton Project Unit III site in Dayton, Ohio — **Unit III Foundation Remnant**
A surviving concrete remnant at the former Unit III property, evidence of structures and site features that no longer stand.Photo by Juliette Killen of Dayton/Vandalia.

Additional concrete foundation and site remnant at the former Dayton Project Unit III complex — **Unit III Site Remnant**
Another surviving concrete feature at the former Unit III site, marking areas where wartime facilities once occupied the property.Photo by Juliette Killen of Dayton/Vandalia.

Wide view across the former Dayton Project Unit III site at 1601 W. First Street, Dayton, Ohio — **Unit III Site Context**
A wider view of the former Unit III property, showing how the surviving wartime buildings fit into the present-day site.Photo by Juliette Killen of Dayton/Vandalia.

Additional surviving building at the former Dayton Project Unit III site in Dayton, Ohio — **Another Surviving Unit III Structure**
A broader view of another surviving structure within the former Unit III complex, reinforcing that the Manhattan Project operation occupied a multi-building site.Photo by Juliette Killen of Dayton/Vandalia.

Industrial exterior view of a surviving Dayton Project Unit III building in Dayton, Ohio — **Unit III Industrial Exterior**
A modern exterior view highlighting the plain, functional architecture of the surviving Unit III wartime buildings.Photo by Juliette Killen of Dayton/Vandalia.

Circular concrete or metal site fixture embedded in the ground at the former Dayton Project Unit III property — **Unit III Ground Fixture**
A surviving ground-level fixture at the former Unit III site. Its exact wartime function has not been established, but it remains part of the physical fabric of the property.Photo by Juliette Killen of Dayton/Vandalia.

Wide perimeter view of the former Dayton Project Unit III complex at 1601 W. First Street in Dayton, Ohio — **Unit III Perimeter and Site Overview**
A wider present-day view of the former Unit III complex and its surviving structures from outside the property perimeter.Photo by Juliette Killen of Dayton/Vandalia.

Historic floor and site plan of Dayton Project Unit III — **Unit III Floor Plan**
Bonebrake Theological Seminary and the surrounding Dayton Project laboratory complex.

Dayton Project Unit III in September 1943 — **Unit III — September 1943**
The former Bonebrake Theological Seminary near the beginning of its conversion into a secret Manhattan Project laboratory.

Dayton Project Unit III in October 1947 — **Unit III — October 1947**
The expanded laboratory complex after several years of wartime and early postwar work.

Historic plan of Dayton Project Unit IV at Runnymede Playhouse — **Unit IV — Runnymede Playhouse Plan**
The Oakwood estate transformed into the Dayton Project’s principal wartime polonium-production facility.

Dayton Project Unit IV Runnymede Playhouse in October 1947 — **Unit IV — October 1947**
Runnymede Playhouse after its conversion from private recreation facility to polonium-processing plant.

Surviving buildings 4, 5 and 6 at Dayton Project Unit III — **Surviving Unit III Buildings 4–6**
Several of the concrete-block Manhattan Project buildings remain at the former Unit III site.

Modern view of the surviving Dayton Project Unit III complex — **Unit III Today**
A modern view of the surviving portion of the former secret laboratory complex.

The Trinity Gadget being prepared before the July 1945 nuclear test — **The Trinity Gadget**
The implosion device prepared for the world’s first nuclear explosion on July 16, 1945.

Postwar Little Boy atomic bomb casing — **Little Boy**
A postwar Little Boy-type casing photographed by the Atomic Energy Commission. This is not the weapon dropped on Hiroshima.

Fat Man atomic bomb physics package being assembled on Tinian in 1945 — **Fat Man Assembly — Tinian, 1945**
The wired physics package of the implosion weapon before installation in its outer casing.

Additional Library of Congress documentation covering the history,
architecture, and operations of the Mound facility.

Open document

The Tennis Court That Built the Bomb