 Use of the codename Silverplate was discontinued in May 1947 . It was superseded by a new codename , " Saddletree " . This was applied to aircraft modifications only . Initially it was intended that Saddletree would refer only to modifications to the B @-@ 29s , but it came to be used for modifications to B @-@ 50 and B @-@ 36 bombers as well . Saddletree modifications included a new bomb bay frame and hoist , and replacing the British FG bomb release with the newly developed U @-@ 1 pneumatic bomb release mechanism . Due to delays in the delivery of the B @-@ 50s , Saddletree commenced in February 1948 . In all , 6 @,@ 000 hours of work was carried out on each of the 36 B @-@ 50s by Sacramento Air Materiel Area . 
