 The initial run of 12 aircraft for the "First Chip" program were converted from the 1952/1953 serial blocks of B-57B aircraft still on active duty, including the two sent to Pakistan as "Pee Wee 1" and "Pee Wee 2".They were delivered one a month through 1964; the last ("First Chip" 12 and formerly "Pee Wee 2") was retained as a test bed in Fort Worth.The next four conversions were to RB-57Ds that were taken out of storage under a follow-up program called "Second Slice", delivered between April 1965 and February 1966.