Those explosions were primarily Viking rockets, I seem to remember, developed for the Navy by a civilian contractor.
Huntsville, home of military rocket development, was supposed to keep hands off the space program, so the available V-2 and Redstone rockets were off limits for the space program.
After Sputnik, the complexion of the space race changed radically. The United States panicked. Ultimately we did what should have been done initially, namely use Redstone rockets to put a satellite in orbit.
All this is from memory, so if I'm wrong on details, c'est la vie.