Since the beginning of the invasion helicopters were the target of attacks with "aerial improvised explosive devices" or home-made bombs.[4] In early 2007, the U.S. Army announced that the Iraqi insurgent groups had developed a strategy for attacking American helicopters.[5] This was confirmed by documents captured from Iraqi insurgents.[6][7] U.S. deputy commanding general Jim Simmons said that the average month in 2006 and 2007 saw about 17 attacks against helicopters.[8] Efforts to reduce losses included more training for helicopter pilots and improvements in tactics and aircraft defenses.