The connection with Groton goes back well before the advent of the nuclear submarine, to when the Electric Boat Company, founded in 1899 to build submarines to John Holland's patents, ran into trouble as a result of the poor climate, post-World War I, for warship construction.

Unable to win further orders from the US Navy (which ordered no submarines from it between 1919 and 1931), Electric Boat succeeded in 1924 in obtaining an order from Peru for four submarines. Until that point, the company had subcontracted construction work on its sub hulls to various existing shipyards, but it was loaded with so much debt as a result of over-expansion to meet wartime demand that sharing profits with another company was no longer an option. Instead, EBC took the decision to expand a factory it owned in Groton, which built diesel engines for submarines, into a full-fledged shipyard. The company history gives no reason for why the decision to select Groton was made, but it was probably a combination of a factory located on the shoreline and the presence there of an existing, skilled workforce. Submarine construction is an unusual skill, especially in terms of fitting large components into very tight spaces, so that likely made the difference.

Source: James S. Reyburn, Electric Boat Corporation pp.6-8.