Adopted in 1880 to replace the Adams revolver, the Enfield MkI was based on an extraction system patented in the 1870s by Owen Jones of Philadelphia. This was similar in practice to the Merwin & Hulbert, with the barrel and cylinder hinging forward while the cartridge cases were held to the back of the frame. This system allowed empty cases to drop free (except the 6 o’clock position one, which often stuck) while retaining any unfired cartridges in the cylinder. Because the extractor star was fixed to the frame, the piece had to be loaded one round at a time through a loading gate (again, like the Merwin & Hulbert).
In 1882 a number of improvements were made to the design and lockwork, including features to prevent the cylinder from rotating freely and to disconnect the hammer when the loading gate was open. This was adopted as the MkII in 1882. A further change was made in 1887, following the death of a Royal Navy sailor whose gun fell out of its holster and discharged upon hitting the hammer. A new safety mechanism was added to prevent this from happening again, and most guns in service were retrofitted with it.
The Enfield was generally not well received, as it was heavy and a bit awkward to handle. It was issued to the Army, Navy, and RCMP, but replaced by the first adopted Webley top-break revolvers in the late 1880s (Enfield MkII production ceased in 1889). Unlike the Webleys and other private-production guns, there was never a civilian version of the Enfield MkI or MkII made, and they are scarcer to find today as a result.