Why changing heavy weapons takes more than training

How long would it take Ukraine to transition to Western heavy weaponry?

About six months if begun immediately, because the change requires an entire supply and maintenance system rather than training alone.

A transition to Western heavy equipment would take roughly six months even if work began immediately. Operator training is only one part of the problem. A new equipment family also needs fuel, ammunition, maintenance, spare parts and the transport network that moves them forward. Building those supply lines into a country at war makes roads and railways as important to the conversion as the weapons themselves.