If you want hard facts, I busted out my copy of Small Arms of the World and found the following:
"In 1903 tests were made with the Vickers, the modified Maxim, so named after the Maxim patents ran out and some few changes had been made. The guns were then being built at Hartford by the Colt's Company. These guns were practically identical as to operating mechanism as the one Maxim had shown at the 1888 trials when he used black powder cartridges. The United States Army adopted the model as manufactured by Colt's to use our standard .30 cartridges. It was designated the 1904 model Vickers. In 1916, as a result of tests made against seven competing machine guns, the Army Board recommended purchase of 4600 Vickers guns, M1915. At the time we did not have one machine gun in the Army which was actually of a type we would care to use on the European front.
Meanwhile, the famous Browning gun had been developed. The heads of the Army were now so impressed with this model that they insisted that no offical adoption be considered for any other machine gun. But in 1917 it was impossible to produce the gun for prompt use. We called on Colt's therefore to manufacture more Vickers with which to arm our forces. Colt's had been producing tooling to produce it for the Russians in 7.62mm. The necessary re-tooling to produce it for the United States .30 cartridge hindered production and it was July, 1917, before initial deliveries were made. Although during the period from then to September 12, 1918, 12,125 of these guns were made. Over 7,000 American Vickers were shipped overseas.
There is a lesson here which we as a nation might learn if we would. It is shown by the figures of World War I, when the Germans at the outbreak if the war had 12,500 of the Spandau-made Maxims ready for service. Remember that we did not have a single acceptable machine gun ready for active military field use then. And at the end of the War we still had very few of our own at the front."
-Small Arms of the World, tenth edition.