Original sentence: The North Koreans began their war against South Korea on June 25, 1950 with a small, obsolescent air force of propeller-driven Soviet aircraft of World War II vintage flown by under-trained and inexperienced pilots
Edited sentence: The North Koreans began their war against South Korea on June 25, 1950 with a small, primitive air force of propeller-driven Soviet aircraft of World War II vintage flown by poorly-trained and inexperienced pilots