 The Fat Man and Pumpkin bombs weighed over 10 @,@ 000 pounds ( 4 @,@ 500 kg ) , so weight was a concern , even with the more powerful engines . Weight reduction was accomplished by removal of all gun turrets and armor plating . This work was done by the 509th Composite Group for the early Silverplate aircraft , but later models were delivered without them . These B @-@ 29s represented a significant increase in performance over the standard variants . 
