All major U.S. off-metals struck in proof are rare. Although undated, this Kennedy Half Dollar is at least 40 years old due to the design style of the hair in the portrait of president Kennedy.
The reverse has a first strike incuse brockage of the obverse. The nickel blank was centered on top of a struck Kennedy Half Dollar when it was struck. Notice that the incuse brockage shows the full portrait since it was struck over the obverse of a struck Kennedy Half. The obverse shows part of Liberty and In God We Trust as well as the entire portrait, since it was struck by the obverse die. A spectacular and unique major mint error.