I await in trepidation your next set. When you capture an enemy Worker, the enemy unit is destroyed (exactly as when you kill a military unit) and a Worker of your nationality spawned in its place. The catch is that the game does not check if the enemy's Worker was a UU or not, it just spawns the default Worker. Those unit upgrade costs are way too high. It will be faster to just build new axes, but the situation being what it is... However, can you really afford even one upgrade, if you're in deficit even at 0% research? Edit: hadn't noticed you had updated the previous post. Hopefully it'll work!