I am "Assuming" your father has passed away?
All I can tell you based on the information you supplied is that your father was an Infantryman and that an 11B5M is a 1st Sergeant E8. This rank was generally the highest "Non-Commisioned" (Not an officer) attained within a Company of approximately 200 men. Often the first Sergeant was referred to as "Top" or "Top-Sergeant" for this reason. This is usually someone who spent considerable time in the military...likely a career?
You can request copies of his service records from the National Archives Personnel Records Center if he has passed away and you are a surviving child. This can be done on-line at:
http://www.archives.gov/veterans/military-service-records/index.htmlWhen filling out the form, you want to be sure to request all available documentation...NOT just his DD214...which it sounds like you already have. Once you receive the documents, one of them will list his duty stations....which will tell you what units he served with and on what dates. From there, you can determine search criteria to possibly find an Association which might have members who knew him.
Good Luck!