Looking at the site on aerial imagery, it is hard not to notice how close it sits to Detroit Metro Airport, which during World War II was known as "Army Air Depot, Romulus," and "Romulus Army Air Field." It also appears that Northline Road, which is normally a straight east-west road, suddenly curves up northwest from the airport to go directly past this place, almost as if it was built as a service road between the two sites. Suddenly it seemed even more likely this facility could have originally been a government base after all.
Looking at an aerial view of the area, Northline Road seems to curve suspiciously toward this site from Detroit Metro Airport, making me wonder if in fact it was originally built that way to serve as a driveway between the two facilities, as is often seen where Nike Missile sites or ammo dumps are often situated near Air National Guard bases, such as Selfridge ANGB. According to Detroit Metropolitan Airport History by local historian Daniel Mason, from 1941 to 1947 the Army Air Corps leased Metro Airport (then called Wayne County Airport), for the purpose of ferrying military airplanes and freight from coast to coast. The Michigan National Guard also shared the airport with Wayne County's Airport Authority from 1930 to 1971. Under the Army's 345th Air Transport Command, the 3rd Ferrying Squadron--comprised of mostly of female pilots--was tasked with flying the various planes.
Looking at historicaerials.com, I see that this angled stretch of Northline Road did not exist on their c.1942 topo map--it is shown as running east-west along the same roadbed that is now called Wabash Street. But Northline is shown as angled steeply to the northwest on their c.1953 topo map, and the east-west grade was being called "Old Northline." What looks to be the Kelsey-Hayes Plant is first shown on their c.1969 aerial photo, so at least the building itself could not have dated from the 1940s, but there could have been a small tarmac or supply yard there.
I emailed local historian Daniel Mason, who specializes in the history of Romulus Army Air Field, to ask if he knew whether this property was ever a government installation. He said he was familiar with the tower in question, but lent his opinion that it was more likely a structure built by the railroad as a switch tower, or for security to keep watch over the switchyard. This makes sense, seeing as that approximate spot is where several railroad spurs branched off to enter the Kelsey-Hayes plant at various points. He also confirmed that my hunch about Northline Road being rerouted was correct, but it had more to do with airport expansion after WWII than it did with the disposition of the Kelsey-Hayes site.
Per a comment from a reader, "bigguy1960," the c.1956 DTE aerial photograph of the site shows what looks like a total of three of these towers along the fenceline of Wabash Street. "It also appears that there is a cut along the fence to allow a vehicle to patrol," he noticed. Indeed, it does certainly seem like they are guard towers of some kind. The plant was apparently under construction in the 1952 aerial photograph, and looking at the 1967 photo, it seems that there were a total of five towers located around the entire perimeter of the plant.
The Army Air Forces in WWII, Vol. 6
Air Transportation, Vol. 6-7 (1945), p. 7
"Where I Came In.." in China, Burma, India, Vol. 2, by Robert James Kadel