We present the first installment of a massive spectroscopic survey of Galactic O stars , based on new , high signal-to-noise ratio , R \sim 2500 digital observations from both hemispheres selected from the Galactic O-Star Catalog of and .
The spectral classification system is rediscussed and a new atlas is presented , which supersedes previous versions .
Extensive sequences of exceptional objects are given , including types Ofc , ON/OC , Onfp , Of ? p , Oe , and double-lined spectroscopic binaries .
The remaining normal spectra bring this first sample to 184 stars , which is close to complete to B = 8 and north of \delta = -20 ^ { \circ } and includes all of the northern objects in that are still classified as O stars .
The systematic and random accuracies of these classifications are substantially higher than previously attainable , because of the quality , quantity , and homogeneity of the data and analysis procedures .
These results will enhance subsequent investigations in Galactic astronomy and stellar astrophysics .
In the future we will publish the rest of the survey , beginning with a second paper that will include most of the southern stars in .