In 1940 Alvarez joined the MIT Radiation Laboratory , where he contributed to a number of World War II radar projects , from early improvements to Identification friend or foe ( IFF ) radar beacons , now called transponders , to a system known as VIXEN for preventing enemy submarines from realizing that they had been found by the new airborne microwave radars . Enemy submarines would wait until the radar signal was getting strong and then submerge , escaping attack . But VIXEN transmitted a radar signal whose strength was the cube of the distance to the submarine so that as they approached the sub , the signal — as measured by the sub — got progressively weaker , and the sub assumed the plane was getting farther away and did n't submerge . The radar system for which Alvarez is best known and which has played a major role in aviation , most particularly in the post war Berlin airlift , was Ground Controlled Approach ( GCA ) . Alvarez spent a few months at the University of Chicago working on nuclear reactors for Enrico Fermi before coming to Los Alamos to work for Robert Oppenheimer on the Manhattan project . Alvarez worked on the design of explosive lenses , and the development of exploding-bridgewire detonators . As a member of Project Alberta , he observed the Trinity nuclear test from a B-29 Superfortress , and later the bombing of Hiroshima from the B-29 '' The Great Artiste ''
Trinity nuclear test
Trinity (nuclear test)
Luis Walter Alvarez