Helmer Hartmann Dahl (17 June 1908 – 29 March 1999) was a Norwegian engineer.
He graduated as an engineer from the Norwegian Institute of Technology in 1931, and was hired at the Chr. Michelsen Institute in 1935. From 1942 to 1945 he was in exile in the United Kingdom. Here he became a part of the Technical Committee of the Norwegian High Command, together with scientists such as Svein Rosseland, Leif Tronstad and Gunnar Randers. The Technical Committee is considered as the precursor to the Norwegian Defence Research Establishment, established in 1946. Dahl worked at the Norwegian Defence Research Establishment from 1946 to 1949, but then returned to the Chr. Michelsen Institute, where he was a research director from 1950 to 1978.
Dahl was also a member of the board of the Norwegian Broadcasting Corporation, from 1945 to 1974. In 1995 he was, as the first Norwegian citizen, awarded an honorary degree at the University of Trondheim.