By Alastair Lawson
The submarine is the latest example of the rebels' technical skills
As the Sri Lankan army advances against Tamil Tiger rebels in the north, it says it is inflicting a devastating blow against their capacity to continue fighting on land, sea and air.
In addition to making significant territorial gains in recent weeks, the army says it has killed or captured hundreds of rebel soldiers.
But it also says it has seized much of the hardware which over the past two decades made the rebels one of the world's most feared - and most ingenious - insurgent groups.
The latest example of their innovative technical skills was displayed on Thursday, when the army unveiled a 35-foot (10.6m) armour-plated submarine it said it had seized.
Three partially completed mini-submarines and a 152mm artillery gun were also captured by troops, the army said.
Experts say that the underwater vessels had been assembled deep in the jungle without technical back-up in conditions that would have required considerable skill.
Observers say the rebels have been forced to make many of the weapons themselves because of a widely applied international arms embargo - many countries label the rebels as "terrorists".
It's thought that the rebels still have several 152mm artillery guns.
At the same time, the Tamil Tigers are up against a government which has raised defence spending to record levels in recent years.
In March 2007 the rebels used two light aircraft - according to the government it might have been one - to drop several bombs on an air force base at Katanayake, north of the capital.
"While there is no doubt that the rebels had the potential to use all these weapons to deadly effect, the fact is that they have all been rendered useless now because their territory is shrinking so fast in the face of the army offensive," retired General Hamilton Wanasinghe told the BBC from Colombo.
"I think the main threat our troops face in the final phase of our offensive - the mopping up period - will only come from small arms fire and roadside bombs."
Military analysts inside and outside Sri Lanka mostly agree with Gen Wanasinghe's assessment that the rebels are now in a position where they will be unable to use their more sophisticated weaponry.
"They are confined to a small area where it's impossible for them to use their aircraft as they have nowhere to take off," says Amal Jayasinghe of the AFP news agency in Colombo.
"They do still control about 30km (18.7 miles) of coastline, but the seas adjoining it are heavily patrolled by the Sri Lankan navy, so any effort to use the few small gunboats they have left are not likely to be successful either."
Chandana Bandara of the BBC's Sinhala service says that the rebels are also thought to have several 152mm artillery guns in addition to some multi-barrel rocket launchers and mortars.
Evidence that they still have artillery was clearly seen on Thursday when troops were shelled from two different rebel-held areas.
The army now has the advantage in manpower and weaponry
There have also been unsubstantiated reports that the Tigers may possess artillery shells or warheads that contain chlorine or phosphorous.
Amal Jayasinghe says that ultimately the rebels have two other last-resort methods of defence.
"The first is civilians," he says. "Thousands are thought to be in the area of conflict but few have emerged from town and villages captured by the army."
Analysts say that means that the army cannot advance further without the risk of killing many innocent bystanders, something which would cause international outrage.
"The second option they have is arguably the rebels' oldest and most deadly tactic," says Amal Jayasinghe. "As the Tigers get pushed further and further into a corner the greater the chances of them using suicide bombers."
"As Sri Lanka's troubled history over the last 20 years has shown, these have been used repeatedly and with deadly effect."