How long did the Manhattan Project take?

The Manhattan Project was a secret research project set in a few locations during World War II. In order to end the war, the American government decided to make a plan to discreetly build nuclear bombs and drop them on Japan so the war would end. First, they warned the Japanese government by trying to warn and negotiate with them, but the Japanese did not want to negotiate or end the war.

Then the American government dropped pamphlets in the cities where they planned the bombings warning the citizens of their imminent danger. Then they established this project in Oak Ridge and other cities. In these cities, engineers began creating the bombs. It took about three to four years to make and continue after the bombings.