1972 Eisenhower Silver Dollar Proof
In 1972 the Mint issued copper nickel circulation strike coins which were struck at Philadelphia and Denver only. It also produced 40% silver Proof coins struck at San Francisco. Finally, it also struck 40% silver un-circulated coins struck at San Francisco which carry an S mint mark but these coins weren't meant for circulation.
Instead the 40% Silver un-circulated Eisenhower Dollars were only sold to collectors. These un-circulated coins were sold in single packs, sometimes referred to as Blue Packs which is the nomenclature used to describe the outside packaging in which these 40% Silver un-circulated coins were sold in.