Two full pages, 4to, on lined yellow legal paper. “…From mid 1944 until the end of the war we developed a system to measure the amplitude and pulse duration of the airblast from a nuclear explosion. We used blast gauges which were derivatives of a gun target system which had been developed at Cal Tech. Our gauges were dropped from a B-29 on parachutes and we received their signals thru a telemetering system on recorders with film cameras recording the data displayed on cathode ray tubes…We were informed on the afternoon of 8/5/45 that we were to take off shortly after midnight on 8/6/45…We took off and flew side by side to Tibbets plane the Enola Gay…We could see the Enola Gay all the way to our primary target, Hiroshima. As we approached the target we turned on our equipment. By a prearranged signal we released our gauges, from our bomb bay, when the Enola Gay released their bomb, the `Little Boy.' Less than a minute later our compartment lit up with a bright white flash and seconds later we were shaken by the blast and a second alter shaken again…”