Although the design looked similar to the Blenheim, it was somewhat larger, with an 18 in (46 cm) increase in wingspan. The fuselage was longer in the nose and taller to accommodate a fourth crew member and the aircraft was considerably heavier. The larger bomb-bay was designed to house a semi-recessed torpedo or an increased bomb load. Due to the increased weight the Bristol Mercury engines on the Blenheim were to be replaced by more powerful, sleeve valve, Bristol Perseus motors. It was soon determined that even with the Perseus, the Beaufort would be slower than the Blenheim and so a switch was made to the larger Bristol Taurus engine, another sleeve valve design. For these engines, chief designer Roy Fedden developed special low-drag NACA cowlings, which exhausted air through vertical slots flanking the nacelles under the wings. Air flow was controlled by adjustable flaps.