While at the time of his death the Red Army was still firmly in the grip of the cavalry, Tukhachevsky had changed the Red Army's mentality quite significantly. While many machinists were being arrested and marshal Budyonny spoke in favour of cavalry influential people, even including the less intelligent marshal Voroshilov, under who Tukhachevsky served and who took part in the arrests, began to question the cavalry's position inside the Red Army. The horse did remain ingrained in the Red Army however. In peacetime cavalry made sense to the Red Army, it was effective in smaller actions and internal security actions, many horse riders were available without requiring significant training and there were the memories of the effectiveness of cavalry during the Civil War, all of which helped the horse in maintaining its central position inside the Red Army. When the Second World War began mixed units were set up which included both cavalry and tanks, these played a central role in use of the deep operations doctrine during WWII.