During the junior year at NROTC MIDN and Core OC's find out what they are going to do in the Navy based on wish list, grades, ASTB and aptitude. The Core OC's put in a service selection just like the MIDN's they are with and compete for designators they desire such as pilot, NFO, SWO and so forth. The day I was notified that I was still a 1390 (pre select fy10 for pilot) the STA-21 resaults came out. I was told that STA-21 and NROTC service selection are one in the same as far as releasing dates. If you think about it getting picked up for STA-21 is similar to a service selection because it is saying you are going to commission and this is what you will do as an officer. If I can help explain this in any other way please let me know.