Underwing pylons were introduced on the D-15-RE and D-15-RA production blocks. These enabled a drop tank or a bomb to be carried underneath each wing in addition to the stores carried on the belly shackles. Fuel changes had to be made to incorporate plumbing for the underwing tanks. Bomb selection increased to two 1000-pound or 3 500-pound bombs, with maximum bombload being 2500 pounds. Alternatively, a 108-gallon drop tank could be carried underneath each wing, adding 150 miles to the P-47's range. Earlier P-47C and D models could be modified in the field to accommodate underwing racks, but the amount of work required many man-hours of effort by maintenance personnel. The underwing pylons had a detrimental affect on performance, and their air resistance cut 45 mph off the maximum speed. However, a redesigned, more streamlined pylon cut the loss to about 15 mph.
Beginning with production blocks D-22-RE and D-23-RA, a larger (13- foot diameter) paddle-bladed propeller (either a Hamilton Standard Hydromatic 24E50-65 or a Curtiss Electric C542S) was fitted to make full use of the additional power provided by water injection. It added 400 feet per minute to the climb rate, but during landings and takeoffs there was only a scant six inches of clearance between blade tips and the ground. .
Blocks D-22-RE and D-23-RA were also provided with a jettisonable cockpit canopy which was activated by the pilot pulling a ring. The hood would then be pushed backward, and the force of the slipstream would then do the rest of the job of pulling the canopy free of the aircraft. A bullet-proof windshield was fitted, and internal fuel capacity was increased.
