General Groves' Memo to Secretary of War Stimson about 'The Test'

On July 18, 1945, General Leslie Groves, the military commander in charge of the Manhattan Project, sent a memorandum to Secretary of War Henry Stimson about the test at Trinity Site. Here are some highlights...

The test was successful beyond the most optimistic expectations of anyone. Based on the data which it has been possible to work up to date, I estimate the energy generated to be in excess of the equivalent of 15,000 to 20,000 tons of TNT; and this is a conservative estimate. Data based on measurments which we have not yet been able to reconcile would make the energy release several times the conservative figure. There were terrific blast effects.

For a brief period there was a lighting effect within a radius of 20 miles equal to several suns in midday; a huge ball of fire was formed which lasted for several seconds. . . The light from the explosion was seen clearly at Albuquerque, Santa Fe, Silver City, El Paso and other points generally to about 180 miles away. . . Only a few windows were broken although one was some 125 miles away. . .

A crater from which all vegetation had vanished, with a diameter of 1200 feet and a slight slope toward the center, was formed. . . The material within the outer circle is greenish and can distinctly seen from as much as 5 miles away. The steel from the [test] tower was evaporated. . .

Groves also relayed the account of General Thomas F. Farrell in the memo to Stimson. Farrell watched the blast from S-10000 - an observation and control shelter 10,000 yards south of ground zero.

Farrell: "The effects could well be called unprecedented, magnificent, beautiful, stupendous and terrifying. No man-made phenomenon of such tremendous power had ever occurred before."

Check out the entire scanned document online at the Truman Presidential Museum & Libray