1. Ever since the end of World War 2, American military officers have gone overseas in large numbers to give advice and training to the military personnels of developing countries.
2. Ever since the end of World War 2, military Ameriican officers have been going overseas in large numbers to give advice and train to the military personnels of developed countries. 
3. Military American officers have been going overseas ever since the end of World War 2 in large number to give advice and train to military personnels of developed countries.
4. To give advice and training in large numbers to the military of developing countries, American military officers have gone overseas ever since the end of World War 2.