The Parker 51, introduced in 1941, is a famous fountain pen. Parker’s period advertising called it “The World’s Most Wanted Pen,” and this assertion was true although a little deceptive; the U.S.A. entered World War II in December 1941, and the War Production Board placed severe restrictions on production of pens for civilian sale. Parker's continued advertising during the war created a demand that took several years to fulfill after the end of the war. The pen was developed for use not with Parker's regular ink Quink, but with a new formula ink, advertised with the slogan, "writes dry with wet ink".
Unfortunately, this new ink's high alkalinity and isopropyl alcohol content were fatally corrosive to the celluloid then used for the bodies of most pens (including the Parker Vacumatic, the company's flagship pen during the 1930s). Making the "51" pen's body and inner cap of a new plastic called Lucite, just coming into use for airplane canopies — and plastering the bottle, cap, and box with warnings not to use the ink in any pen "not even other Parker pens", except for the "51" — solved the corrosion problem somewhat.
The pen and the ink were both named "51" to mark 1939, the company's 51st year of existence, during which development was completed (U.S. design patent No. 116,097). By giving the pen a number instead of a name, Parker avoided the problem of translating a name into other languages.
The "51" was revolutionary at the time, with its hooded, tubular nib and multi-finned collector, all designed to work in conjunction with the pen's proprietary ink, allowing the nib to stay wet and lay down an even line with either the ultra-fast drying ink or more traditional inks.[1]
With various refinements, the "51" stayed in production until 1972. The most significant design change came in 1948, with the introduction of the much improved Aerometric filling system.[2] At the same time, Parker reformulated its ink, reducing the alkalinity, adding a selection of brilliant colors, and calling the new product Superchrome. Like the "51" ink, it also came with a warning that it should be used only in the Parker "51" (or its new little brother, the "31"), but the warning was more discreet.
The pen's resemblance to the P-51 Mustang, a fighter plane used extensively during the war, had no bearing on its name; but Parker took advantage of the coincidence by comparing the pen and the plane in its advertising. Additionally, a pilot who is suspected of falsifying flight records in his logbook in order to overstate his actual experience is said to have logged "P-51 hours," relying on the ambiguity of the term "P-51" to avoid directly confronting the suspect.
The "51" is among the most popular pen models sought out by pen collectors, and in 2002 Parker issued a lookalike model called the 51 Special Edition. In 2004, the larger and heavier Parker 100 was released.