[1][2][3] Before World War II, he researched valence theory, polarimetry and related optically active compounds.
Johnson's Birmingham colleague Mark Oliphant directed Rudolf Peierls and Otto Frisch (refugee physicists also at Birmingham) to investigate if indeed such a weapon was feasible and in March 1940 Frisch, using Peierl's formula, got an alarming result which confirmed that a small mass of uranium-235 could have a devastating effect; the Frisch-Peierls memorandum was circulated secretly by Oliphant and immediate action taken to try and secure supplies of uranium ore. What came to be called the MAUD Technical Committee was created in response to the Frisch-Peierls memorandum.
At Birmingham, the committee was led by Peierls assisted by Johnson, Nobel Prize winner Norman Haworth and, in 1941, Klaus Fuchs, who was later exposed as a Soviet spy.
Haworth led the chemists studying the properties of uranium hexafluoride; Johnson's experiments resulted in a paper describing how it attacked various materials.
From 1958 to 1964, he was the Director of the Explosives Research and Development Establishment at Waltham Abbey, part of the Ministry of Aviation, when he retired.