1942P Copper Nickel Jefferson Nickel.
Wartime design with large mintmark.
This is the only known 1942P Jefferson Nickel
Struck on a prewar Copper Nickel planchet

The 1943 copper Lincoln may be more famous

but the ​​

Copper Nickel 1942P, 1943P, 1944P Jefferson Nickels are the only ones known!

Most valuable of the unique Copper Nickel war nickels:
1943P Copper Nickel Jefferson Nickel.
This is the only known 1943 Jefferson Nickel Struck on a prewar Copper Nickel planchet.

1944P Copper Nickel Jefferson Nickel.

This is the only known 1944 Jefferson Nickel Struck on a prewar Copper Nickel planchet