Five-cent pieces had been struck by the United States Mint since 1792. They were the first coins struck by Mint authorities. These half dimes (originally spelled "half dismes"), were struck in silver. The alloy used was originally .892 silver with the remainder copper; in 1837 the silver portion was increased to .900.
The Civil War caused most American coins to vanish from circulation, with the gap filled by such means as merchant tokens, encased postage stamps, and United States fractional currency, issued in denomination as low as three cents. Although specie (gold or silver coins) was hoarded or exported, the copper-nickel cent, then the only base metal denomination being struck, also vanished. In 1864, Congress began the process of restoring coins to circulation by abolishing the three-cent note and authorizing bronze cents and two-cent pieces, with low intrinsic values, to be struck. These new coins initially proved popular, though the two-cent piece soon faded from circulation. On March 3, 1865, Congress passed legislation authorizing the Mint to strike three-cent pieces of 75% copper and 25% nickel.
In 1864, Congress had authorized a third series of fractional currency notes. The five-cent note was to bear a portrait of "Clark", but Congress was appalled when the issue came out not bearing a portrait of William Clark, the explorer, but Spencer M. Clark, head of the Currency Bureau. According to numismatic historian Walter Breen, Congress's "immediate infuriated response was to pass a law retiring the 5¢ denomination, and another to forbid portrayal of any living person on federal coins or currency." Clark only kept his job because of the personal intervention of Treasury Secretary Salmon P. Chase.
Mint Director James Pollock had been opposed to striking coins containing nickel but in view of the initial success of the copper-nickel three-cent piece, he became an advocate of striking five-cent pieces in the same metal. In his 1865 report Pollock wrote, "From this nickel alloy, a coin for the denomination of five cents, and which would be a popular substitute for the five cent note, could easily be made ... [The five cent coin should be struck in base metal] only until the resumption of specie payments ... in time of peace ... coins of inferior alloy should not be permitted to take the place permanently of silver in the coinage of pieces above the denomination of three cents."
Longacre's two-cent piece; its design was the basis for the Shield nickel.
Industrialist Joseph Wharton had a near-monopoly on the mining of nickel in the United States and sought to promote its use in coinage. He was also highly influential in Congress. His friends there, though they had failed to obtain the metal's use for the two-cent piece, had been more successful with the three-cent coin. Pollock prepared a bill authorizing a five-cent coin of the same alloy as the three-cent piece and a total weight not to exceed 60 grains (3.9 g). At the committee stage in the House of Representatives, the weight was amended to 77.19 grains (5.00 g), ostensibly to make the weight equal to five grams in the metric system[a] but more likely so that Wharton could sell more nickel. This made the new coin heavy in comparison to the three-cent copper-nickel coin. The bill passed without debate on May 16, 1866. The new copper-nickel coin was legal tender for up to one dollar, and would be paid out by the Treasury in exchange for coin of the United States, excluding the half cent, cent and two-cent. It was redeemable in lots of $100 for banknotes. Fractional currency in denominations of less than ten cents was withdrawn.