In 1861, Whitney accepted a U.S. contract to produce 40,000 U.S. "M1855" rifle-muskets. What Whitney had in mind under this contract and what the War Department demanded were two different arms. Whitney's product was similar to U.S. M1855 rifle-musket, but differed in a number of respects. The 40" barrel was .58-caliber, but rifled with 7- rather than 3-grooves and adapted to English P1853 socket bayonet he had been using on his Enfield derivative rifle-muskets. Initial rear sight, while similar to U.S. M1855 type, was slightly shorter having a 2.3125" base. (On later production, Whitney substituted a shorter 1.25" long base, with a single pierced leaf sight). Nosecap was made of pewter and followed Enfield pattern rather than being malleable iron of U.S. M1855 pattern. On later production, Whitney also substituted brass winged lock screw washers from his Enfield derivative series. Lockplates for these arms were drawn from complete Maynard locks made at the federal armories in 1858 and 1859, but later rejected for flaws. Upon these plates Whitney stamped "E. WHITNEY / N. HAVEN", as on his early Connecticut contract M1861 derivative rifle-muskets. Except for the letter/number code, the barrels are unmarked. Examples are known whose stocks bear indications of issue to 8th Connecticut Infantry during the Civil War, suggesting Whitney may have sold the few made to Connecticut under his first state contract. Arms with these regimental marks should command a premium over unmarked arms.