How did classic masters like Alekhine and Anderssen practice tactics? How did classic masters like Alekhine and Anderssen practice tactics? Surely there was no chess.com or chesstempo at that time. How did the masters back then manage to increase their tactical awareness?
In Joosep Grents's wonderful biography on Paul Keres, there is a brief first-hand account of tactics training in that time period. For background, Paul was a contemporary of Alekhine and almost played him for the World Champion title, but the match never materialized.
Here's what Paul Keres had to say about training tactics in the 1930s (emphasis mine):

I used correspondence games, above all, for experimental purposes,
often opting for very risky opening lines and attempting, at all cost,
to create complicated positions which I could use to train my tactical
skills... It is easy to notice a bias toward tactics in these games,
while there are still considerable problems apparent in solving
strictly technical problems.

The article notes that at one time Paul was playing more than 100 correspondence games at once.