The contract for the XP-61D had a supplemental clause which called for the the development of two XP-61E aircraft. The XP-61E was to be a bomber escort version of the Black Widow. Two P-61B-10-NOs were selected for the conversion (serial numbers 42-39549 and 42-39557). Since the P-51D Mustang had proven itself to be more than adequate as a bomber escort, the XP-61E project ended up on the back burner at Northrop, and the conversion was not completed until March of 1945.
The XP-61E retained the 2250 hp R-2800-65 Double Wasps of the P-61B. However, the central fuselage nacelle was completely revised, almost nothing remaining the same. Most notable was the use of a tandem two-seat cockpit with a bubble canopy. The third seat in the rear of the night-fighter Black Widow was eliminated. The radar in the nose was removed and replaced with four 0.50-inch machine guns with 300 rpg. The four 20-mm belly cannon were retained. Additional fuel tanks were added to the crew nacelle, bringing the total internal fuel load up to 1158 gallons. A ladder was installed in the left side of the extreme aft section of the crew nacelle. The first aircraft had a bubble canopy which swung to the left when it was opened, but the canopy on the second aircraft slid to the rear when opened. The four nose machine guns in the first plane were in a box arrangement, whereas those in the second airplane were laid out in an approximately horizontal line.
The second XP-61E (42-39557) was wrecked in April 1945 when a test pilot prematurely retracted the landing gear during a high-performance takeoff. The plane settled back down onto the runway, breaking off its propeller blades and coming to a screeching halt as it slid along on its belly. The pilot walked away from the incident, but the aircraft was a total loss.
Further testing on the first XP-61E showed that it had a distinct performance advantage over the night-fighter Black Widow variants, attaining a maximum speed of 376 mph at 17,000 feet. However, the performance of the XP-61E was not as good as the latest fighters then entering service. In particular, it was not nearly as fast as the North American XP-82 Twin Mustang, which had been specifically designed for the escort role. The XP-82 had flown for the first time on April 15, 1945 and had exhibited maximum speeds of no less than 482 mph at 25,100 feet. Consequently, there was no further consideration of the XP-61E as an escort fighter.