An early AI, and the birth of the transistor
Vacuum tubes were all well and good, but they were bulky, hot, power hungry, and prone to failure. Early on, artificial neural networks showed promise, as even if tubes broke while it was running, it would keep working. Meanwhile, the transistor is invented, and the unreliable tubes slowly became obsolete.
Here is an article about the SNARC, the first artificial neural network.
Here are a couple of videos of Marvin Minsky talking about the SNARC.
Here’s a documentary on the invention of the transistor.