Your right about that, they have somewhat a very dynamic and broad role to play in U.S. security, you can occasionally spot an article in All Hands or Navy times about USCG protecting ABOT or patrolling the Persian Gulf, they operate around the world just as the DOD branches do. From Alaska to training missions with CGs and Naval units in South America.
Even send vessels and personnel on training missions with countries in Europe. USCG makes certain that tax payers money isn't put to waste and our nation's security and safety on our coastal water ways in very well granted.
Not to mention that all sea going vessels in some form have to register with the USCG, and they track stolen vessels and help recover them if possible if they are still in U.S. waters, and if not if the vessel is recovered in foreign waters, the CG will try to make the hand off.