Tactical, compact, service, subcompact, makes it confusing as hell! I BELEIVE, my gun is a service, compact .45 ACP. Compact refers to the grip length, and service refers to the barrel. Here's how I understand it:
Service = 4" barrel
Tactical = 5" barrel
Compact = short grip
Subcompact = 3" barrel, and short grip
Now here's where it gets confusing. The .45s have a different naming scheme for the options if you click on XD .45 ACP or compact on their website. They refer to them by barrel length instead of tactical and service, but they come up with the same part #. If you click on service or tactical, they show ONLY standard grip guns in all calibers (including .45 ACP), again, the part numbers are the same under multiple listings. You can only see the compacts under compact, or XD .45 ACP. Something I think is totally retarded is they only offer compacts in .45 ACP! Too dang confusing, and completely disorganized.