2nd class (junior) year is generally when the various exchange programs take place, whether the exchange is to a different service academy, or to a foreign country. However, some majors (esp chemistry) are not conducive towards participation in exchanges. There are also several summer foreign exchange/training programs.
One other note: the Men's and Women's Glee Clubs give periodic concert tours. These include a foreign tour ~every 3 years or so. Last spring break, the WGC were guests of the Brazilian Navy for the week. They visited the Brazilian Naval Academy, and they met the Brazilian CNO. I believe that the MGC toured in Chile and Argentina the year before that.