The Canadian Forces are investing in a new high-tech shell to be used in Afghanistan. But at $150,000 per round, it could be the most expensive ammunition ever fired by the military.

"It's like shooting a Ferrari every time you use one of these things," Steve Staples of the Polaris Institute told CTV News on Thursday.

"These are incredibly expensive weapons. And really, it's overkill for the kind of mission we're doing."

Defence Minister Gordon O'Connor estimates Canada will have poured $4 billion into the Afghanistan mission by 2009. Just sending a squadron of Leopard tanks to the region costs $190 million.

But supporters argue the shell -- called the Excalibur -- is worth the added expense. U.S. defence contractor Raytheon promotes the shells as "the next-generation family of projectiles," and the U.S. military already uses them in Iraq.

"The forces on the ground have been pretty content with the weapon, in the sense that it has met the needs at this level, and they're looking forward to the future developments that Raytheon is working on at the moment," said Justin Tkach of Jane's Strategic Advisory Services.

According to Raytheon's pamphlet on the Excalibur, the "GPS-guided projectile provides accurate, first round fire-for-effect capability to all current and future 155-mm howitzers."

The shell uses software to direct it within 10-metres of its intended target, even when fired from up to 40 kilometres away, apparently minimizing unintended casualties. Standard shells are usually accurate to within 50 metres.

"Its accuracy will reduce collateral damage and permit its use close to friendly units, thus increasing employment flexibility," the pamphlet states.

It's that increased accuracy that caught the military's attention, said retired major major-general Lewis MacKenzie.

"You could imagine if they could find a group of Taliban that are about to ambush a Canadian convoy, or any other convoy at a range of ... 40 kilometres is an extremely valuable resource," he said.

Military analysts say standard shells fired from a howitzer can cost between $2,000 and $10,000. Dawn Black, the NDP defence critic, says that rather than spend $150,000 on a single round, Ottawa ought to spend it on more aid in the region.

"We have to supply clean water," she said. "We have to supply electricity so that they can get on with some kind of economic development. And unless the people of Afghanistan see these kinds of differences, we're not going to win the hearts and minds of these people."

It's unlikely that argument will change the minds of battlefield commanders, who want any technology that improves their fighting power.

"I don't have a business plan when I'm fighting and trying to save Canadian lives and get rid of some pretty nasty people. I don't think about the bottom line," said MacKenzie.

With a report by CTV's David Akin