As Nato defence ministers meet in Brussels to consider the Western alliance's post-Afghanistan capability needs, a new piece has just been added to its growing ballistic missile defence (BMD) jigsaw.
This month, the USS Donald Cook, under Commander Scott Jones, became the first of four US Navy BMD-equipped destroyers to be forward-based in Europe, at Rota in southern Spain. And the BBC was aboard to see it.
The Donald Cook comes equipped with an upgraded Aegis defence system, the associated powerful SPY radar panels on the ship's imposing superstructure, and 90 vertical launch cells to carry the all-important Standard SM3 interceptor missiles, as well as cruise missiles and other weaponry.
The US Navy Secretary, Ray Mabus, who was on hand with other US and Spanish officials at Rota to witness the Donald Cook's arrival, described the Aegis system's missile defence capabilities as "unmatched".
Mr Mabus also underlined the operational significance of forward-basing the four ships in Rota, making them more responsive in a crisis because they would not need to cross the Atlantic to be on station. He said it would enable the US Navy to be ready "when it counts, not just the right place at the right time, but the right place all the time".
Nato is changing gear as it comes home from combat in Afghanistan and refocuses on what future capabilities it will need. It officially adopted missile defence to protect its territory and populations from at least limited attack in 2010.
The Nato Secretary General, Anders Fogh Rasmussen, a missile defence advocate, called the Donald Cook's arrival a step forward, and insisted that the proliferation of ballistic missile technology was a real threat.
But the programme has been controversial. Russia remains unreconciled. And, while the system is under Nato auspices, most of the hardware and the bulk of the outlay have come from the United States. What the United States calls its phased adaptive approach to missile defence includes the ships, an early warning radar in Turkey, and two interceptor bases in Romania and Poland. Nato, for the most part, provides the host facilities, and the command-and-control centre.
"For most Nato European states, they're happy to go along with the phased adaptive approach to missile defence, but most of all because it's a way of binding the Americans to European security," according to Professor Malcolm Chalmers, of the Royal United Services Institute in London. "So far at least, I don't think the Europeans see the Iranian or Middle East threat as being as serious to Europe as the Americans do."
But Professor Chalmers said that could change, and European governments could come under more public pressure to field such defences in the future.
As it is, with Nato entering an uncertain period and with growing concern about other security issues in and around the Mediterranean, Nato is also looking at focusing increasingly on its maritime forces. So it suits both the United States and the alliance also to emphasise the non-BMD, multi-mission capabilities of the Donald Cook and her sister ships.
"Ballistic missile defence is just one mission area in the wide range of missions that this ship can execute at one time," say the Donald Cook's second-in-command, Commander Charles Hampton. "We train a lot for maritime security operations as well as theatre security when we pull into port - it's always been a big part of the Navy, pulling into port, working with our allies, and I certainly expect that to continue on this deployment."
Among the ships' capabilities will be operating as forward bases for ship-launched unmanned air vehicles - drones.
And there is another timely message in the Donald Cook's arrival. The destroyer is a near-9,000-ton honeycomb of steel compartments and passageways, brimming and humming with advanced equipment, and housing more than 300 officers and crew. She, and the new families who will be settling in and around Rota, certainly seem like a powerful symbol of a new US commitment to Europe at a time when many Europeans are worrying that Washington's attention is wandering elsewhere, to Asia. And a likely theme of the forthcoming Nato summit in Cardiff in September will be renewing "transatlantic bonds".
"It seems counter-intuitive if we were leaving Europe, and we are not, that we would decide to spend considerable sums of money to forward-deploy four modern fighting ships at Rota," says Robert Bell, the US Defence Secretary's representative in Europe, based at Nato. "In that sense it's strategically significant because it's a reminder that, although we're rebalancing some of our military capabilities to requirements in the Pacific, we are not in any way leaving Europe."
The proponents of maritime power might argue, however, that - unlike the large land forces that the United States based in Europe in the past - warships can, if required, be quickly redeployed elsewhere.
Just how the USS Donald Cook is employed while in European waters may be far from certain. But she is likely to be busy.
The missile defence debate has come a long way since the Star Wars vision - some said fantasy - of President Ronald Reagan in 1983. Even now, the technology for that is beyond reach. But the message from Nato is clearly that alliance missile defence is up and running, albeit in a much more limited way than President Reagan envisaged. Working systems like that on the Donald Cook exist. The controversy has not disappeared by any means, but it has perhaps lost a little of its previous political and diplomatic toxicity.