The continual development of weapons and rocket and artillery launches is not a choice but a must as long as U.S. threats against Pyongyang continue.That's according to North Korea's main newspaper Rodong Sinmun.The paper claims that no other country in the world is under constant threat like North Korea is and says that the North needs weapons upgrades and displays of military might to deter such threats.The paper went on to criticize the recent Ulchi Freedom Guardian exercise between South Korea and the United States.North Korea has long denounced such annual drills as a rehearsal for an invasion of North Korea.Seoul and Washington say the exercises are purely defensive.