Star Trek: 10 Secrets Of Enterprise NX-01 You Need To Know

Among several structural components carried over from the Akira-class to the NX-class was a pod mounted between the ship's engines. While on the Akira-class, this pod was a weapon's module which could be seen firing photon torpedoes in Star Trek: First Contact, a similar pod on the NX-01 served a very different purpose.

According to Doug Drexler, the pod on the NX-01 was actually intended to help to show that ship was far less advanced than the Constitution-class Enterprise of The Original Series:

Mike [Okuda] and I decided, to make the ship more primitive, that the warp field that it generated was not symmetrical… it was asymmetrical and that created a problem because it was dangerous. That pod was a symmetrical warp governor, basically that additional generator could shape the warp field for it.

Despite this very technical explanation for the pod, this feature was never mentioned on screen, but was one of many details included in the ship's construction to make what Doug calls the "ironclad" of the Star Trek Universe:

It looks like an ironclad next to the Constitution-class. The Constitution-class is sleek and smooth like a marine animal, it’s not like any spaceship you’ve ever seen before. The NX-01’s got plates on it and it’s primitive next to the Constitution-class.