As American involvement in World War 2 (1939-1945) grew, so too did its need for long-range reconnaissance. This need was only partly solved by conversion of existing Boeing B-17 "Flying Fortress" and Consolidated B-24 "Liberator" four-engined heavy bombers but these designs still had their inherent range limitations. With the introduction of the Boeing B-29 "Superfortress" strategic bomber in 1943, all that changed for now the United States Army Air Forces (USAAF) now had, in its stable, a versatile performer capable of reaching the ranges expected of it - particularly across the vast expanse of the Pacific Theater.
This initiative led to the service using 100 of the early-form B-29 and B-29A production models for the conversion process which essentially involved removal of bomb-carrying facilities though retaining the remote-controlled machine gun-armed defensive armament. Since the reconnaissance-minded Superfortress would be flying at high altitudes, this was negligible. Between Air Technical Service Command and the Fairchild Photographic Company, a viable camera-laden equipment package was developed for the reworked bomber, giving rise to the "F-13" variant. Original B-29 models were designated simply as F-13 while B-29A production forms modified to the reconnaissance standard became F-13A - the "F" was used to indicate the platform's intended "photographic" role. Conversion work was handled at the Continental Air Lines Denver Modification Center.
The photo-reconnaissance equipment consisted of three K-17B, one K-18, and two K-22 camera systems installed in at the rear crew compartment along with a B-3 "Driftmeter" sighting device. The rear fuselage was slightly modified to accommodate the units and cutouts had to be made along the ventral and side faces of the airframe in this section. The cameras were operated by a dedicated crewman - the Photo-Navigator - whose position remained at the nose of the aircraft. The Photo-Navigator and the Cameraman were additions to the standard B-29 operating crew of eleven. Additional camera equipment could be installed in the forward bomb bay if the mission necessitated it. In lieu of this, photo "flash bombs" could also be hauled.
To cover the long-range requirements of the sortie, the bomber was given additional internal fuel stores for a greater operational reach. These were installed in the rear bomb bay.
Overall, the basic form-and-function of the bomber remained including its four-engine arrangement spread out over the wide-spanning wing mainplanes. The definitive Boeing large-area, rounded tail fin was also retained as was the heavily-glazed nose section of the aircraft. A tricycle undercarriage provided the needed support during ground-running. Power stemmed from 4 x Wright "Duplex Cyclone" air-cooled radial piston engines providing 2,200 horsepower each and driving four-bladed propeller units. Up to 12 x 0.50 caliber Browning air-cooled Heavy Machine Guns (HMGs) could be used to defend the aircraft from all angles, most fitted to powered, remotely-controlled turrets along the fuselage's dorsal and ventral lines.
The initial F-13A operational model was delivered to Saipan in mid-October 1944 and immediately went to work against the heart of the Japanese Empire providing critical photo-graphic evidence on enemy strength and positions - namely in and around the Japanese capital of Tokyo. From there, the F-13/F-13A fleet was used extensively from land bases in China and the Pacific until the end of the war.
After the war ended in 1945, the series was redesignated as "FB-29"/"FB-29J" until 1948 when they were redesignated, yet again, to become the "RB-29"/"RB-29A" to serve under the newly-minded United States Air Force (USAF). By this time, the defensive machine gun arrangement (save for the rear-facing tail emplacement) of the aircraft were deleted to save on weight and proved little use at high operating altitudes - often times out of reach of Japanese interceptors.
At least six of the F-13A lot were reworked with Wright R-3350-CA-2 fuel-injected engines under the developmental designation of "YB-29J" before becoming certified under the "RB-29J" mark. For December 1950, the 91st Strategic Reconnaissance Wing relocated its RB-29s to Yokota Air Base in Japan to support United Nations actions in the Korean War (1950-1953) where RB-29s and RB-50s (the latter based in the modified B-29 Superfortress bomber, the "B-50") continued to provide the needed long-range photo-reconnaissance role in wartime. When their slower speed proved a liability, the jet-powered RB-45C ("Tornado") bomber conversion was used instead.
Quite notable is the last sortie of the war was completed by an RB-29A.