Possible error coin? Big “u” cut into it, 1943 nickel

So tell me, how would this be an error coin? Did somebody sneak into the mint in the middle of the night and carve a U into it? More likely it was done with a mallet and a punch. What makes your coin worth a dollar and change is that it's a wartime silver issue. See the mint mark over Monticello on the back? The P is for Philadelphia and they only did that 1942 to 1945, with nickels that are 1/3 silver and 2/3 manganese.