The following screenshot shows the addition of large form changes and chamfers on the tail and some cutting away of the initial primitive, marked by arrows. A drum on the side of the tail has been added and marked with yellow poly-loops.
An Extrude outward and inward helps build the hull. Poly-loops help mark key areas.
The selected polygons in the following screenshot are where the ship airlock will project out. It's good to shape the area where an Extrude will be added so it fits well into what surrounds it.
And here's the airlock, as shown in the following screenshot. Its shape is easy to make using Extrude, Chamfer, Inset, and Cut, the most common tools we've looked at so far.
Similarly, it requires just a series of Extrude and Inset steps to add the panels on top of the hull. These are on the center line, so the new polygons facing the Mirror line should be removed and lined up to X = 0.0.
The following screenshot shows a close up of the lower edge...