They can trail an antenna behind the boat underwater that receives low frequency radio waves carrying short signals that basically tell them to come up to a higher depth to receive a longer message.
If you like this, you’d probably really enjoy the hobby of ADS-B tracking. If you have a spare Pi sitting around, you can get an SDR and decent starter antenna for under $100. It’s also a fun entry point into other radio and satellite stuff. Airplanes.live is a good place to start.
Wasn’t the Model T the first mass-produced automobile? Wouldn’t surprise me if the early 20th century electric cars were basically handbuilt by dozens or even hundreds of different manufacturers.
The Model T is the first assembly line produced automobile. Mass production significantly predates the Model T. Generally, the production of guns in France in 1765 using standardized parts is generally considered the first mass produced item.