They won't make any difference. There aren't enough of them being delivered to Ukraine. The only hope is that they are a foot in the door and if Russia doesn't start WW3 over 14 Challengers, then it probably won't start WW3 over 21 Challengers. And if it didn't start WW3 over 21 Challengers then it probably won't start WW3 over 35 Challengers, etc., etc. In various deserts in the United States, we have nearly 4,000 older generation Abrams tanks in long term storage. If we shipped a thousand of them to Ukraine and protected the fuel pipelines into the area to make sure they could stay fueled, that would make a difference. However, going from zero American tanks straight to a thousand American tanks might start WW3.