Swimaster
Voit Corporation is one of the oldest sporting goods companies in the world. It was founded by William J. Voit of Worthington, Indiana (1881-1958) in 1922. As such it was one of five original United States diving gear makers: Swimaster, US Divers, Healthways, Voit and Dacor. Although Voit exists today, they don't produce fins anymore, just simple snorkeling masks. Voit purchased company Swimaster in the early 1960s and it overtook its model " Orca Fins " and renamed it to "Duck Fins", a name which became a synonym for this type of fins, while also keeping a brand name Swimaster (see writting on bottom left corner of fin).
Source: http://www.spearfishing-museum.com/F08.htm