In light of the UK's exit from the EU a few disturbing questions must be asked....
1. Will the UK remain the US' most important partner?
I'm not sure. The US has already indicated that its trying to pivot to the Pacific. In that region Australia, Japan and S. Korea are much more important than the UK could ever hope to be. India, Singapore, and the Philippines are also higher on the rung than the UK.
2. What about in the Middle East and Africa?
Again, I'm not sure. The French and Dutch have more enduring relationships in the region. Even Germany with its arms sales is as consequential as the UK.
3. Will they retain their seat on the UN Security Council?
You can see a vigorous argument being made that the current model for the Security Council is outmoded. China, France, the UK, the US and Russian Federation makes it a Euro-Centric organization. I personally could see another country replace them. An easy argument could be made for India (Pakistan would howl) because they're a fast growing economy and have a huge population not to mention independent. Either way I predict that you will see fights over their inclusion on the Security Council and instead of even France keeping its seat you'll probably see a restructuring with the EU gaining a seat and the UK being kicked off for another country.
4. Will they stay with the F-35 program?
Again not sure. What I do know is that costs for them just ballooned. Best scenario is that they get a massive cut in the order. Worst case for the F-35 is that they prioritize domestic production and push for an Advanced Typhoon.
5. What about the UK Armed Forces as a whole?
For better or worse the UK will turn inward. I expect a TREMENDOUS fall off in deployments and for a time a "Fortress UK" being erected while they sort this out. Foreign entanglements haven't been positive in the past and will be worse in the future.
6. Ok, we've heard your warmup, give us the pitch! Will the special relationship survive?
Doubtful. The UK just gave up its most important bargaining chip and value to the US. Acting as a moderating force for the US in the EU. The EU will probably face the same troubles as the UK. A serious turn inward, and a risk adverse attitude toward foreign adventures.
In summation this is a watershed event. Globalization has taken a massive hit with this vote. Everything from economics to foreign relations will change because of it.