 Complete the following phrase:  The R-1s were assigned to the cavalry brigades, two platoons of two or three tankettes apiece. All eighteen belonging to the Cavalry Corps were grouped into the ad hoc Korne Mechanized Detachment during the opening stages of Operation Barbarossa, but all were out of commission by 1 October. Twenty-nine of the original thirty-five were allocated to the six cavalry divisions redesignated from brigades on 25 March 1942 that successfully participated in the German 1942 summer offensive, codenamed 