What is the 1943 penny?
Do you mean a 1943 penny, since there were over a billion struck - ? Anyway, copper was a strategic material needed for ammunition casings. To free up copper for the war effort, in 1943 the Mint decided to strike cents out of zinc-plated steel. The coins quickly proved to be unsatisfactory for a number of reasons - they were easily confused with dimes, the zinc coating turned dull gray[*], and eventually the steel core began to rust. In 1944 enough copper scrap was available from used shell casings that copper coinage was resumed. As a result, 1944 and '45 cents are sometimes called "shell case cents". A few leftover copper blanks intended for 1942 cents somehow got mixed in with steel blanks intended for '43s, and were struck with that date. These famous "1943 coppers" sell for thousands of dollars today. Unfortunately, they are also often counterfeited so most of the suspected specimens that are now found turn out to be fakes. Similarly, a few steel blanks were struck in 1944 so there are "'44 steels" but these are less sought-after than the '43 coppers. [*]The gray color caused people who were unfamiliar with the coins' composition to erroneously refer to them as "lead" pennies.