The Parker 51 is a fountain pen first introduced in 1941. Parker marketed it as “The World’s Most Wanted Pen,” a slogan alluding to restrictions on production of consumer goods for civilian markets in the United States during World War II. Parker's continual advertising during the war created demand that took several years to fulfil after the end of the conflict.
The pen and the ink were both named 51 to mark 1939, the company's 51st anniversary, during which development for the pen was completed (U.S. design patent No. 116,097, U.S. Patent 2,223,541 filed). By giving the pen a number instead of a name, Parker avoided the problem of translating a name into other languages.
