 The B-29 did enjoy limited success postwar as a flying testbed, being used with NACA to carry the early rocket aircraft (X-1, X-1A, D-558-2, and other test aircraft), prototype jet engine testing, electronic test ships, and High Altitude Atmospheric tests.During the early 1970s, NASA (the redesignated NACA) sold their P2B-1S ("Fertile Myrtle") and for numerous years this aircraft flew under civil registration until it was grounded by spar corrosion.The majority of the surviving B-29 came from airframes that had either been designated (with the US Navy at NAWS China Lake), initially, as target-tow aircraft, then unmanned target aircraft, finally as a ground target (the last B-29 destroyed was in 1981 more than six years after a ban had been placed on further using these aircraft as targets).