By Simon Johnson and Alistair Scrutton
STOCKHOLM (Reuters) - With a depleted military lacking anti-submarine helicopters and intelligence so far based on civilian sightings, Sweden's hunt for a supposed U-boat intruder has an element of farce pointing to the difficulty of wrapping up the mission successfully.
More than 200 troops, stealth ships and helicopters have scoured waters off Stockholm since Friday in Sweden's biggest military mobilization since the Cold War, after reports of foreign "underwater activity" - suspected to be a Russian sub.
Stockholm's huge archipelago is now forecast to suffer severe storms, hampering the search. Sweden's military said on Wednesday that it would be scaling down the hunt, with some ships returning to port, although it remained on high alert.
The Nordic state and European Union member, which last waged war two centuries ago, spends more on its generous family welfare benefits than on a military that accounts for around 1 percent of GDP after years of steady defense cuts.
Sweden has fewer big fighting ships than Norway, which has half its population. In 2008, Sweden sold some of its anti-submarine helicopters and pensioned off the rest. Local media reported that several were now in a Swedish museum.
With the Ukraine crisis heightening tensions, Sweden's defense capability was already under the spotlight. When Russian warplanes staged a mock bombing run on Sweden last year, Danish jets belonging to NATO based in Lithuania took to the air to shadow them after Sweden's air force was caught napping.
That led the military to question the country's ability to defend itself for more than a week against a Russian attack.
The armed forces have so far had five sightings of a suspected "submarine" in the archipelago, including one grainy photograph which showed some ripples and a dark object.
"All come from tips from the general public," Admiral Anders Grenstad told reporters on Tuesday. "We have our own information, but that has been classified as so low (grade) that it hasn't been reported."
"WHISKEY ON THE ROCKS"
Despite scepticism about the sightings, many Swedes recall the Cold War when the navy repeatedly chased suspected Soviet submarines along its coast with depth charges.
In 1981, in an incident known as "Whiskey on the Rocks," a Soviet nuclear Whiskey-class submarine was stranded near a major naval base deep inside Swedish waters after it ran aground, causing a diplomatic standoff.
The Swedish navy, with five anti-submarine corvettes, is still regarded as skilled in anti-submarine warfare. It was recently invited for war games with the United States.
"No matter how capable your ships, they can only be in one place at one time," said Christian Le Miere, senior fellow for Naval Forces and Maritime Security at the International Institute for Strategic Studies in London. "The problem is not that they aren't well practiced at this kind of thing, but that they may not have the kind of size necessary."
Even with modern ships, the task is huge. The archipelago, a popular holiday destination, consists of some 30,000 islands and a maze of narrow channels and inlets. The military said it has received some 100 "tips" about sightings since Friday.
Supreme Armed Forces Commander Sverker Goranson is pessimistic that the navy can ever find a submarine. "I want to remind you that, historically, we've never managed to do it and nobody else has either," he told reporters.
Paranoia has crept in. Reports of a black-clad man wading through waters in the archipelago turned out to be a local trout fisherman rather than any member of Russian special forces.
One local newspaper illustrated an online report of "heavily armed troops" heading towards a site in the archipelago with a picture of what turned out to be a chartered boat filled with reporters from a rival newspaper.
There have been many false alarms in the past. In 1995, then-Prime Minister Ingvar Carlsson said that the military on several occasions thought it had detected submarines only to find many of the underwater sounds were made by minks.
Fast forward to 2014. "The best navies in the world and the largest navies in the world would struggle to find this submarine, if it is indeed a submarine," said Le Miere.
(Additional reporting by Sven Nordenstam; Editing by Mark Heinrich)