This upgrade had to be retrofitted to missiles that had already been shipped .
Air Force officials argued that they only needed to add valves to the LOX lines on the grounds that the RP - 1 could not detonate without oxidizer .
This upgrade had to be retrofitted to missiles that had already been shipped , but Air Force officials argued that they only needed to add valves to the LOX lines on the grounds that the RP - 1 could not detonate without oxidizer .