I doubt that very much. The U.S. already has the cooperation it needs from Germany via NATO, of which the UK is a leading member and will continue to be a leading member.America is not going to sever its relationship with Britain. But the relationship will slide down its list of priorities, maybe below those with France and Germany
As recent history in Iraq shows, the EU has a history of not walking the walk when it comes to oil security...America and the EU will agree on most issues and disagree on others. By and large, they will find themselves on the same side in diplomatic matters involving Russia, militant Islam, security of oil supplies,
Again, I doubt that. The only military asset on the Atlantic coast is the strategic deterrent fleet and that would be relocated to Plymouth.Another consequence of the Brexit fallout on the special relationship is the possibility of Scottish independence. The loss of its Atlantic coastline diminishes Britain's strategic importance to the US military.