The US/Spain agreement for Rota to become a part of the Shield anti-missile system will heighten the military threat to this area in times of hostilities.
Had Gibraltar increased its military capability, the Spanish would have lost no time in arguing that it posed increased risks to Spain. But neither Gibraltar nor Britain will react against Spain in the way Spaniards would have reacted against Gibraltar. Instead, Foreign Office policy is to urge the MOD to emasculate its military presence at Gibraltar so as not to upset Spain and to make a political deal more plausible.
The Shield system is defensive in nature because it seeks to alert about enemy missiles fired at European targets. "With four Aegis ships at Rota, Nato is significantly boosting combined naval capabilities in the Mediterranean and enhancing our ability to ensure the security of this vital region," said the US defence secretary.
Although the Western argument is that the system - of which Rota is only a part - is not aimed at Russia, Moscow lost no time in reacting angrily against it.
A highly sophisticated early warning system for Turkey announced last month, aimed at countering ballistic missile threats, provoked an angry response from neighouring Iran, warning that the installation would escalate regional tensions.
As regards the Rota move, military experts in Spain say that by increasing its strategic importance, Rota is also increasing its potential as a target for enemies of Nato.
Plans for the defence Shield project were approved by Nato leaders in Lisbon last year. The US ships now announced for Rota form part of an initial deployment of a Nato-designed anti-missile shield and are equipped with radar and Aegis missile-intercept systems.
Although the four US ships will be based at Rota they will come under the Nato/US command in Naples, Italy.
Where does all this leave Gibraltar? Nato has long been urging Britain to increase, and not decrease, its military presence at Gibraltar by improving surface and sub-surface defence of the Strait.
Nato has taken the view that "current defence capabilities deployed by the UK in Gibraltar are inadequate or non-existent and that any further delay in improving defence and choke point control facilities at Gibraltar will prevent Nato from making best use of this strategic position."
Secret documents show that during 1980-84 the aim was to provide for an integrated system which would have included modern early warning radars with capability against low flying aircraft and missiles, point and area defence missiles, surface to surface missiles.
A document marked 'Secret UK Eyes' says that, considered in isolation, the geographical position of Gibraltar provides an excellent base for the employment of technologically advanced weapons and equipments such as remotely controlled minefield, active and passive surveillance equipment operating above, and below, the surface together with their associated weapon systems.
It is an often rehearsed argument that in tension or war, Moscow - if they were involved - might endeavour to control or deny the use of the Strait to Nato by a variety of measures, such as mines.
The depth of water in the Strait would indeed allow both anti-surface ship and anti-submarine mines to be laid. Most Russian warships have the ability to lay mines, which can be remotely operated.
It has been recent American policy to keep the Russians at bay, by providing assurances and elements of cooperation. The Americans see current potential enemies more in the North African littoral. Countries that can develop long-range missiles that can target Europe attract close interest from Washington.
There is a clear interest to keep North African countries near the western entrance to the Mediterranean within the Western fold or at least neutral, in peace and specially in war.
But as Gibraltar's military importance wanes, and that of others in the region increases, the Rock can be demoted in military terms. In 2002, it was the MOD that scuppered the planned joint sovereignty deal because they, and the Americans, wanted Gibraltar to retain the status quo in respect of the military.
And the Spanish view, then and now, centres in gaining a military foothold in Gibraltar.
That remains the political game today. The importance of having or not having control over territorial waters, the ability to deploy ships and aircraft, the usefulness of having a friendly population...these are some factors that come into play.
The role Gibraltar continues to play for Britain, and indeed for Nato in a less visible fashion, keeps the crunch away. But the more important others in the region become, the greater the chances of Gibraltar's special and time-honoured military importance being subsumed.