On March 14, 1947, the Navy took over four B-29-BWs for long-range search missions. The designation P2B-1S was assigned. They were assigned Navy Bureau of Aeronautics numbers as follows:
Boeing B-29-90-BW Superfortress 44-87766 to USN as P2B-1S BuNo 84031
Boeing B-29-95-BW Superfortress 45-21787 to USN as P2B-1S BuNo 84029
Boeing B-29-95-BW Superfortress 45-21789 to USN as P2B-1S BuNo 84028
Boeing B-29-95-BW Superfortress 45-21791 to USN as P2B-1S BuNo 84030
Later, one of the P2Bs (84029) was modified as the carrier aircraft for the Douglas D-558-II Skyrocket high-speed rocket-powered research aircraft. The P2B aircraft was named "Fertile Myrtle" and carried the NACA number of 137. The bomb bay was extensively modified to carry a D-558-II nestled underneath the belly. The research aircraft was dropped in flight from the bomb bay cradle, and the rocket engines were fired once the plane had fallen free of the P2B.
The first D-558-II launch took place on September 8, 1950 with test pilot William B. Bridgeman at the controls of the research aircraft and George Jansen at the controls of the B-29. A series of Skyrocket launches took place over the next few years, each one further exploring the outer reaches of the flight envelope. The D-558-II exceeded Mach 2 for the first time on November 20, 1953 with test pilot Scott Crossfield at the controls. The last Skyrocket flight took place in December of 1956.
Former P2B-1S 84029 "Fertile Myrtle" was eventually sold to a civilian owner, a museum in Oakland, California. This was the only example of a flyable B-29 ever being sold by the Air Force to a civilian operator. This B-29 was flown on rare occasions under the civil registration N91329. After many years of inactivity, it was sold to the Kermit Weeks Aviation Museum of Miami, Florida. It was transported there disassembled in 1987. It was registered with the Weeks Museum as N29KW.