The only way I can think of to do this while maintaining the outer shield as a stroked path would be with clipping masks, but unless maintaining strokes is a requirement, I believe using masks would be more complicated than necessary.
If it is required to maintain the outer shield's stroke as a stroke, then this answer won't help you.
Personally, I would convert that outer shield's stroke to a compound path with a fill. You should be able to accomplish this by selecting the outer shield, and then going to
Object > Path > Outline Stroke. That should create a group containing the fill as its own path, and what was previously the stroke as another path. You'll need to
Object > Ungroup (Ctrl/Cmd+Shift+G) those objects so they are each individually selectable before proceeding.
Once this is done, I think you should be able to just use
Minus Front from the
Pathfinder panel. Do this by following these steps:
First draw a path between your top and bottom horizontal black bars:
Then select both that path, and your outer shield path, and click the
Minus Front button from the Pathfinder panel:
Then you'll have the gap you wanted:
Repeat those last couple steps on the other side, and I think you'll be done.