Vacuum tube op amps were important in the development of electronic analog computers in the early 1940's. Unlike today's, the early ones had a single input and an inverting output rather + and - inputs. The circuit design was complicated by the need for direct coupling and high stability.
In the 1950's Heathkit made a cute little analog computer
with a total of something like 70 tubes. I would love to get my hands on one of them. They come up on ebay once in a while, but are way out of my price range.
Paul