A high-capacity compound transmission (200) of lighter weight and/or shorter axial length than comparable prior art transmissions is provided. The compound transmission of the present invention utilizes main and auxiliary section countershafts (324, 362) which are coaxial and define a countershaft assembly supported solely by bearings in the transmission housing (214) forward and rearward end walls (214A, 214B) and by a single bearing carried by a minimal intermediate housing wall (214C). The mainshaft (346) is supported solely by tapered surfaces at the forward and rearward ends thereof, which abut complimentary tapered surfaces on or carried by the rearward end of the input shaft (16) and forward end of the output shaft (358). The auxiliary countershafts (362) may be generally tubular (362D) to allow for rear mounting of main section-driven PTO devices.