"The U.K.'s commitment to Estonia is long and enduring," Williamson said. "Over the past year, we have seen how our armed forces have developed a partnership, working closely together through NATO's enhanced Forward Presence (eFP). Some people doubted that it would be so effective and work so well. What I think we've seen in Estonia is how effective it has been."

According to the British defense secretary, what the two allies have seen is an integration of forces from across Europe with those of Estonia, and a real understanding of the latter's military and strategic needs. The U.K. will be serving the Baltic Air Policing operation out of Estonia's Ämari Air Base next year, and the two countries are actually exploring how to strengthen their bilateral relationship and how they can stand shoulder to shoulder as some of the very closest allies.

"Our history, our involvement goes back to 1918, when the Royal Naval Forces arrived here on Dec. 12," Williamson recalled. "That commitment is so incredibly important to us today. Estonia has been one of our closest friends and allies over the last few decades. As our forces and Estonian forces fought in Afghanistan together, we developed a real understanding, a clear partnership and a real bond between our nations. That is certainly something that we believe we will build upon and will be enduring for the next hundred years."

Williamson stressed that the U.K. leaving the EU is not about Britain turning its back on the world. "Quite the reverse — this is our opportunity to strengthen those relationships that we have had with countries, not just over the last few years, but for decades and, indeed, with Estonia, a century now," he said.

"How do we make the relationship better?" Williamson continued. "How do we ensure that people understand that Britain, when it leaves the European Union isn't turning its back on European security?" According to the him, the eFP work in NATO is absolutely critical to reinforcing that message.

"And when we do look at NATO — this is an organization which is probably one of the most important organizations for guaranteeing security in Europe," said the British defense secretary. "And our commitment to it is not going to waver for one moment. Indeed, as we leave the EU, over 80 percent of NATO forces will be provided by countries external to the EU, and our commitment to it is going to be very long and enduring."