They can conduct thorough backround checks on the spot? Who knew!
Hire in haste, repent at leisure.
The offers may be “contingent on passing the background check”.
Background checks are always post hiring. They need to put you on the payroll first so they can start you gathering the information. The job will not be in a classified area until after your clearance comes through, usually around 6 months later.
This is common and sometimes resulted in people being “ice boxed” put to work on really non-essential things while waiting for the clearance. They could put these people on inventory jobs for example when they should be making parts.