You can go to Colt.com and under Customer Services, there's a window that you can put the serial number in and it will tell you the year of manufacture.
That one comes back "1918 Model 1911 Military" .
BUT, a word of caution, make sure it's a Colt frame. A lot of 1911s were pieced together over the years. Post a picture and these guys can tell you what you have.