While U.S. Space Force thus far has split National Security Space Launch (NSSL) between SpaceX and United Launch Alliance (ULA), the service plans to have one more provider by the end of NSSL Phase 3 to guarantee Space Force can reach high-priority orbits when needed.
It’s funny, because back on Reddit, I suggested that the US Air Force (now the Space Force) should’ve picked three launched providers: SpaceX, ULA and Northrop Grumman. That’s because only SpaceX had a working rocket for that proposal at the time. The other two were just gambles, so you probably should’ve picked all three options to give you the best shot at having dual launch capabilities. Instead, they went with just two, SpaceX and ULA. ULA’s rocket has still not launched because, surprise!, it was a gamble that ended up way behind schedule. So the Space Force really only got one rocket out of the deal.
Now they seem to have learned their lesson. They’re likely to pick three separate launch options to maximize their chances of getting dual launch capabilities.