Is this what you’re trying to achieve on the right?
There was no need to explode the sections of the turning to modify them. You could create the torpedo shape outside the group, cut it to the clipboard, open the group for editing and paste the shape in place. Use Intersect Faces and erase what you don’t need. Then repeat for the next group.
You could save yourself a bunch of work if you had made the section a component instead of a group.
If you would complete your profile (like I’ve asked you many times to do) so we knew which version of SketchUp you are using and what operating system, I could give you more specifics about the steps.