One of the most famous errors is the 1943 copper cent.
The U.S. government, in order to save copper for the war effort during World War II issued only steel cents coated with zinc.
What a surprize when a copper 1943 penny showed up in circulation.
Evidently a copper planchet from 1942 fell into the 1943 steel/zinc bin.
This one shown is the most fabulous one you will ever see. A 1942 copper penny was struck over by a 1943 nickel.
(All others are a 1942 blank planchet struck over by a 1943 die intended for a steel cent)
This coin tells the full story of how the 1943 copper cent occurred.
In this case, instead of a blank planchet falling into the 1943 steel/zinc bin, a previously struck 1942 penny fell into the 1943 nickel (5 cent) bin!
The original 1942 date is still barely visible. The 1943 date from the nickel stamping is clearly visible.