Question: When did the manhattan project began and end?
Disambiguated questions and answers: question: Based on the initial thoughts of the project, when did the Manhattan project begin and end?
Based on when the project was being worked on, when did the Manhattan project begin and end?
answer: Began 1939, end 1946
Began 1942, end 1946
Natural Questions answer: From 1942 to 1946 (from the Wikipedia article "Timeline of the Manhattan Project")