Elgin was my father's favorite brand. A tank watch has a rectangular case, as opposed to a round one.
This one's been around the block a few times and the face needs cleaning, but I actually know a little bit about it. It's from 1954 because the back of the case has a name inscribed on it (probably a retirement or service award watch, back when companies did this sort of thing). The little logo under the Elgin name is the Durapower mainspring logo.
Acquired: 2018
Circa: 1954
Origin: USA
Type: mechanical
Features: Durapower mainspring
Current condition: runs fine