Corrected entry: The military used Hummers in the movie. H1 Hummers were not made until 1992.
Corrected entry: At the end of the movie, Bumblebee is seen talking to Optimus Prime and also showed fireballs falling to earth. In the 2007 Transformers movie, Optimus Prime and others didn't arrive on earth until the early 2000's.
Correction: This film serves as a soft reboot, ignoring many elements of the previous continuity.
Corrected entry: In the landing scene with Bumblebee it says it's 1987. But you see H1 Humvees pull up. Humvees were not used by the military until 1989 in Panama.
Correction: HumVees have been in use by the military since 1985. https://time.com/archive/6686223/a-brief-history-of-the-humvee/. They weren't used in combat in until 1989, but the Humvee was already developed and being used by the military by this time, even discounting the fact that this isn't our reality, what with it having Transformers in it.
Correction: The HMMWV (other wise known as Humvee) began production in 1983. Therefore there were military variations around in 1987. The civilian Hummer H1 was built in 1991.