Below is a link to the rules for AIS from the USCG . Not just oceangoing ships that are required to have AIS in use. Most tugs are required to have this installed aboard. I see a lot of tugs in my local port area via AIS data on Shipplotter. Not many pleasure boats using AIS at this time.
You won't find many military vessels using AIS. Some Commanding Officers many use AIS when entering or leaving port, but will turn it off quickly when in open waters. These vessels don't wish to broadcast to the whole world their positions
Automatic Identification System IMO Carriage Requirments - USCG Navigation Center
Larry