In July 1861, Whitney entered a contact with U.S. Navy to produce 10,000 rifles of "Plymouth Pattern". So called after U.S. Navy warship, whereupon the first Harpers Ferry trial rifles had been developed. New Navy rifle borrowed many of its characteristics from French M1846 "carbine a tige". Overall length 50" with 34" long barrel bearing a saber bayonet lug, with guide extending nearly to the muzzle on its right side. Bore was .69-caliber, rifled with 3 broad lands and grooves. Rear sight copied French M1846 and M1859 styles, i.e. it has an elevating ladder but no sidewalls. On early production, sights are serially numbered to rifle's serial number (appearing on breech plug tang). Barrels bear standard U.S. inspection marks on left quarter flat and production date ("1863" or "1864") on top of barrel near the breech. Two lock markings have been encountered. Earlier production uses flat beveled plate marked with date "1863" on its tail and an eagle surmounting a panoply of flags and trophies over name "WHITNEYVILLE". In later (after serial no. 3,000) lock's tail is marked "1864" and stamping forward of hammer matches that on U.S. M1861 Whitney contract rifle-muskets, i.e. a small eagle over "U S" and "WHITNEYVILLE" in forward projection of the plate. Inspector's initials (F.C.W.) appear on barrel and in a cartouche on the stock.

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