Only one operational unit transitioned to B-26s during the war. That was the 73rd Bomb Squadron in Alaska that traded in their old B-18s in early 1942. All others 22nd BG, 38th BG, 42nd BG trained on them prior to the war or were stood up as B-26 units from the get go. Exception being the 17th BG that was converted from B-25s to become one of the two B-26 training units in 1942, before handing that job off and going to North Africa later that year. 1942 was the worst year for B-26 accidents as thousands of newly graduated pilots were thrust into an unforgiving high performance twin with zero prior twin engine experience. The early short wing birds, B-26 and B-26A and early B-26Bs that formed the core of training units had the early R-2800-5 engines that were only rated to 1850 BHP at takeoff. They also had a lot of issues with prop failures and weak landing gear. In Alaska, based on the accident reports that I have seen (Tip to aviationarcheology.com for making these available at a reasonable price) most accidents were weather related, with landing accidents being the next biggest offender. Of the landing accidents, material failure was a major cause - burst tires, hydraulic failure or failure of landing gear to properly extend or lock. A couple crashes were due to too much speed, not enough runway. Only a couple were due to running out of altitude before reaching the runway.