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Now You Know, August 2023

Updated: Oct 10, 2023

Project ELSIE

By Sara Gray, Technical Information Specialist, NSWCDD

As one of “the history people” for the Dahlgren base, I’ve been able to see some cool things Dahlgren does now and has done in the past. One that is in my top five has got to be the ELSIE

blocks. They are these huge concrete blocks in the woods on Tisdale Road, and I feel like Indiana Jones trekking back there to see them. Nature has slowly taken over the blocks, a couple have trees taking root in them, and some have formed small stalactites.

They’re all part of a testing facility for the ELSIE Project. After World War II, specifically around 1948, the Atomic Energy Commission (AEC) tasked the Bureau of Ordnance (BUORD), who tasked Dahlgren with this case. The idea was to develop a light case (Light Case…LC…Elsie. Get it?) for the atomic bomb. It had to be light enough to be carried by Navy carrier-launched aircraft but still ground-penetrating for tactical strikes on hardened underground targets. Overall breakdown of the responsibilities for this project looked something like this:

BUORD Overall Design and Development

Naval Gun Factory Gun Barrel

White Oak Safing, Arming, and Fuzing

Sandia National Laboratory Handling Equipment and Aircraft Saddle

AEC Uranium

Dahlgren Testing and Evaluation of Ballistics

Dahlgren was the obvious best choice for the actual testing of the case. It was the premier organization for gun and bomb testing, and the team there had proven itself with the development of a “sewer pipe” bomb. The ELSIE cases had to be tested by a simulated airdrop. Rather than send airplanes up to 50,000 feet every time they wanted to do a test, the Dahlgren team used a gun. The device had to accelerate but not exceed a certain G-load level, so several barrels were modified to fit this requirement. The general arrangement of the ELSIE test site can be found here. As the device went down the barrel, charges helped create a slow acceleration but still achieve the terminal velocity. One of the barrels modified for these tests actually still exists on base. It is currently stored on Main Range. The device was fired into the ELSIE blocks, concrete targets that are thirty or forty feet thick.

The actual lab work done on these cases was in the Butler Hut, a prefabricated, 40- by 100-

foot, windowless building specially acquired from the War Reserve. This building is none other than today’s Building 492. It was converted to the mailroom in 1956. It had a concrete vault to store the test bombs, and that is still around today as well. Only about ten to fifteen people worked in the building. The demanding project required about sixty hours a week, including weekends. Each person had to have a Q-level clearance, Q being the code word for clearance to work on the design and development of atomic weapons.

Besides clearance level, physical security for the project was high. The Butler Hut was surrounded by a tall chain-link fence with floodlights and was guarded around-the-clock by Marines. To gain access to the building, you had to see a Marine in one office to get the key to another building with the safe that held the key to the Butler Hut. You went to the building, honked your car horn, then stood in the headlights if it was dark. An armed Marine would come to you to check on your clearance. If the alarm was tripped, it would be a minute or less before guards surrounded the whole building. These Marines were frequently put to the test. An “invasion” team, usually from Indian Head, would come down the river by boat, land on shore, and attempt to hang a handkerchief on the fence and escape without notice.

The high-level security granted employees a small amount of authority on base. Only specifically-cleared employees were granted access to the building. Even the base captain was not allowed access. And when the Fire Chief came to inspect the building, he too was denied access and told that if the building caught fire, just let it burn. The authority wasn’t even restricted to physical access. One time, Wes Meyers, a civilian scientist in charge of the ELSIE project, was speeding from the Butler Hut to the test site (there was a temperature component to some of the tests), and a Marine chased him the whole way. Sharing the incident years later during an interview for the base’s 100th anniversary, Meyers recalled:

…he accused me of going 50 miles an hour, and I told him it was faster than that. It was 55.

It was as fast as the jeep would go. He said, “Well, I’m going to take you in.” I said, “You’re

going to go right over there and go in that building and stand there and not make another


Yeah, I’d love to see the officer’s face when you try that next time you get pulled over. But for the ELSIE project and Wes Meyers, rules and regulations stated that when a test was happening, the person in charge had complete authority to do what he considered necessary. And speed was necessary.

Perhaps another reason for the high security was the danger brought on by the materials used in the bombs. About the only difference between the final version of the weapon and the version tested at Dahlgren was that the Dahlgren tests used either normal or depleted uranium, primarily the U-238 isotope. Special health people were sent to the base from Los Alamos to monitor if there were any radiation hazards involved. If it were spilled, it spread readily and was very difficult to control. Once there was a spill (by a man from Los Alamos), and he had to go through a special cleansing process to get it off his hands. If P-239, plutonium, was spilled, it could spread across a table, down the legs, across the floor, and onto the ceiling. The group kept buckets of axle grease around to stop such an accident from getting worse. Such dangerous material meant that none of it could be lost, and everything had to be accounted for down to the fraction of a gram. On one occasion, a device was lost out into the water. They had to mark where it landed in the river and send in a team of divers to retrieve it.

Fun anecdote: when Dahlgren received a shipment of the uranium, the team would take some sailors with them to help load and unload the boxes of uranium. The boxes were only 8-inches square, about a foot high, but they weighed about 100 pounds. Sailors were always very surprised to try and pick up a little box that was so heavy!

The ultimate ELSIE design was a Mark 8. It was much lighter than the Mark 1 “Little Boy” at only 3,230 pounds (Little Boy was 9,000 pounds) and measured in at 9.7 feet long and 14 inches in diameter, half the diameter of Little Boy. Its yield was probably 20-50 kilotons. The light weight meant that it could be carried on naval attack aircraft, including the AD-4B Skyraider, the AJ-1 Savage, and the FJ-4B Fury. Operation Buster-Jangle in 1951 confirmed the ballistic tests at Dahlgren: the Mark 8 was a suitable subsurface weapon. It went into production in February of 1952. Forty bombs were in the stockpile before the Mark 8 was replaced by the Mark 11, later renumbered 91, in 1956. The Mark 91 was also tested at Dahlgren and remained in service until 1960.

Once the Mark 91 entered service, Dahlgren’s involvement in the atomic weapons development program ended. Overall, gun-assembly bombs were overtaken by guided missiles with nuclear warheads. Dahlgren moved on to other projects, and the jungle slowly took over the remnants of one of our small parts in atomic warfare.

About the Author

Sara Gray works for NSWC Dahlgren in the Technical Library & Research Center. She has undergraduate degrees in History and Historic Preservation and a master’s in Management.

A version of this article was previously published as an NSWCDD blog in October of 2017. Reused with permission.

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