The Enfield Pattern 1913 was actually in .276 caliber.  The British were impressed with the performance of the 7mm Mausers used against them, during the Boer War in South Africa.  The Pattern '13 incorporated some Mauser design features and a reduced bore size (from .303).  The out-break of war in 1914 made a change of weaponry unrealistic.  A war time expedient was to have the new Enfield made in the U.S. in .303 caliber.  The Pattern 1914 Enfields were built by Winchester, Remington Arms and (Remington) Eddystone.  Feed problems and lack of parts interchangeability kept the British from issuing the American made Enfields in large numbers to front line troops.  The Pattern '14 did see use as a Sniping rifle and for reserve and training purposes during two World Wars.  (The Pattern '14 later was very popular with British Target Shooters).  The venerable S.M.L.E. proved its worth during WWI.  At Mons (Belgium), the German Army believed they were facing overwhelming British machinegun fire.  In reality, it was "Kitchner's Contemptibles" working the bolts of their S.M.L.E.s that brought the Schlieffen Plan to a halt.
  The U.S. was the true beneficiary of the Pattern '14 when it was revamped as the U.S. Model 1917 Enfield in .30-06.  This was another and brilliant war time expedient, necessary due to inadequate supplies of 1903 Springfields.