The Spanish Army at that period had just fought the Americans in the Spanish-American War, and as you know they stayed out of WWI. Due to lack of funds and ability to rearm after the Spanish-American War, the Ejercito of the WWI era was pretty much still armed with the same weapons as during the Spanish American War. The primary Rifle was the Mauser 1893 short rifle (and the later development 1916). This rifle, in caliber 7 x 57mm, was still pretty much state of the art in 1914-- it compares favorably to the US 1903 Springfield and the German M98 Mauser, though using a slightly smaller bullet. The Model 1916 was essentially a shortened Model 1893 with a straight stock. The quality of these rifles is shown by the fact that many were converted to 7.62 mm NATO caliber in the 1950s. There was also a carbine version of the 1893, called the model 1895. It is likely (though I have no documentation of this) that reserve arsenals included still older weapons, including the Model 1871 Single Shot in caliber 11mm and the Model 1891 Mauser in caliber 7.65 x 57mm. A wide variety of revolvers would have been in use, most of Spanish production. The Spanish purchased the Bergmann Models 1903 and 1908 in 9mm Bermann-Bayard, produced in Belgium (the third Army in the world to issue a semi-automatic pistol). The Spanish later adopted the Campo Giro Model of 1913 in caliber 9mm Bergman-Bayard (9mm Largo). A modified version of this was issued in 1916 as the Model 1913-1916. These pistols were generally produced by the Unceta Company of Eibar. The C96 (broom handle) Mauser was available at that time, and was later popular in Spain, but I have found no evidence that it was officially adopted by the Spanish Army during WWI. I have read that during this period the Spanish adopted the Maxim gun (machine gun), but I cannot lay my hands on a reference for that at present. Sorry not to discuss artillery, etc., but I have no references on that. Attempts by the Spanish to build up the Navy were hindered by their policy of purchasing much materiel and heavy guns from the British, which was reluctant to sell many of these items during the War. References include Ezell, "Pistols of the World" and Smith, "Small Arms of the World".