Well, I have to offer some corrections to all those fans of the line through where I once lived:
1) The Naugatuck Valley runs north from Bridgeport, not New Haven. There are road connections between Naugatuck and New Haven but no rail. People who want to go to New Haven by rail go south to Bridgeport, then east on Metro North. The geology is all wrong for a direct route -- no railroad would try to go over Bethany Mountain or cut grades through Woodbridge, given the alternative of following the Naugatuck River.
2) The Naugatuck Valley continues from Naugatuck north to Waterbury, thence to Winsted; it does not go to Hartford. Hartford is served by Amtrak through Wallingford, Meriden and Berlin (one valley over), with the beginning of that branch in New Haven.
3) Naugatuck is, indeed, the city which gave its name to the Nauga. Naugas were a promotional gimmick of Uniroyal, Inc., which once had three plants in Naugatuck, including one making coated fabrics (Naugahide). The other plants were a chemical facility and a tire-reclaim plant. Today, only the chemical plant remains. Rail traffic was (and is) appropriate to these facilities, and my guess is that during the world war, business at the reclaim plant would have been more than Uniroyal (then United States Rubber Co.) could have handled, since the Japanese had cut American access to the rubber supplies of Southeast Asia, and America needed all of the scrap rubber it could find.
4) Waterbury no longer is, but once was, eastern hub of the nation's brass industry, was served by rail and later by truck accordingly. During the World War, Winchester-Western had a large cartridge plant there with specially built buildings bearing detachable roofs designed to channel any explosions upward rather than outward -- interesting modeling. Also, Scoville Manufacturing (makers of small appliances like mix-masters) was in town, had a rail spur I think, but this was removed by the time I moved to the area. Full histories of all of this are contained in special collections at the Silas Bronson Library on Grand Street -- you have to ask to see it, but other than that, I recall the librarians being very accommodating.
5) North of Waterbury, in the Oakville area, were several brick warehouse-like structures which were used for textile finishing and distribution, and these had rail spurs which I do not think are used any longer. A lot of the cheaper K-Mart type dresses and lingerie came from here.
6) Platts Mill Road was located between Waterbury and Naugatuck and was home to an industrial concern with a spur. But, my memory fails re just what this business was. It may have been a wire company.
7) The town south of Naugatuck is Beacon Falls (not Beacon); the railroad passes on the far side of the Naugatuck River, with Route 8 (a superhighway with stop lights!) passing through downtown. Beacon Falls at one time had a Uniroyal warehouse in it and also was home to the Homer D. Bronson Company, a hinge-manufacturing firm since relocated to Winsted. These hinges were used for everything from small cabinets to diesel trucks and aircraft, and while I think Homer D. used only trucks, it is an old firm and would have needed freight hauling appropriate to its products and finishing processes (primarily electroplating). Beacon Falls also has yielded its share of aggregates, which is why a lot of people take this town for granite. If there were rail connections here, they were long gone by the time I went to work in the area in 1972.
8) There would have been additional rail facilities at Derby and Shelton, both south of Beacon Falls and Seymour. Shelton had several large factories, including a chemical plant which eventually was arsoned for the insurance (the plot fell apart when the perps tried to pin it on the Weather Underground, and the FBI quickly detected the ruse).
9) As far as I know, there never were any rail lines into Prospect, which is due east of Naugatuck. The town was a bedroom community to Waterbury for a long time but did have a small industrial park near the Naugatuck burrough line. This park was near the top of a long hill, but to my knowledge, the town always was called Prospect, not Prospect Hill. I do know that one of the firms located in the industrial park made stranded electrical wire and thermocouples for the defense department. This company however, used trucks for transport.
10) Maybrook, Cedar Hall, and Hancock Bridge are names unfamiliar to me, although I am not that knowledgeable about the northern portion of the valley. Most certainly, they are not the names of any towns. The one large firm I recall being located north of Oakville was Whyco, which did electroplating. As far as I know, they were served by truck, but of course whatever was brought to the factory was metal and therefore heavy. A pretend rail spur would not be inappropriate here.
11) The area north of Oakville even today is relatively undeveloped, largely agrarian, and quite beautiful, especially in the area where Route 8 cuts into the mountains on the way from Waterbury up to Winsted and the Berkshires.