Initialism of United States Ship.
"The USS and U.S.A. are both common abbreviations used to refer to the United States."
plural of US
In plain English: USS is an abbreviation for United States Ship, which is how the U.S. Navy officially names its warships.
"The car was covered in mud and needed to be washed immediately."
Initialism of United States Steel (a steel company)
"The USS stock price dipped after the company announced a merger."