In 1942 the mints produced nickels from nickel (P and D) and from silver (P and S). It was the start of the War Nickel series. The more valuable circulation finds are typically the silver war nickels, but the 1942 D in an XF or higher state is a more valuable find. I used to CRH nickels and attempted to build a roll set for each date/mm and 1942 D proved difficult thus far (I'm on the east coast). So I find saving them genuinely more enjoyable than finding war nickels from that same year.