Atomic engines are the most powerful engines by mass that can be found in human space, but this also makes them the most power hungry, heat producing, and expensive. Atomic engines are rarely seen on merchant ships, and even the Navy only starts using them during the war after the introduction of their mark II ship variants.
With the exception of A120 and A125 engines, which can be found in a few outfitters located in the Paradise Worlds region, these powerful engines can only be found being sold in the Deep.
The Human atomic engines category holds within it the only reverse engine outfit in the game, called the AR120 Atomic Thruster. The stats of the AR120 are the exact same as those of the A120, only they fire in the front of a ship instead of out the back. The description for the AR120 is "For pilots who want to be able to pull fancy tricks that most ships are not capable of emulating, a reverse thruster allows a ship to accelerate backwards, without needing to turn around. Because a reverse thruster must be facing forwards, it must be installed in the weapon section of your ship instead of the engine section."