WASHINGTON — The weight of the U.S. army's new armoured vehicle significantly restricts the flight range of the C-130 cargo aircraft that transport it, congressional investigators have said.

In fact, under certain conditions the investigators said the weight of the Stryker vehicle makes it impossible for the military cargo planes to take off.

Canada announced last year it was buying 60 of the vehicles, which are made by GM Defence in London, Ont.

The Strykers were intended as a replacement for German-made Leopard I tanks.

Critics of the Canadian decision to buy the Stryker pointed to a 1998 study which concluded use of such vehicles would be a disaster.

Experts said the Stryker is underarmoured and mounts a gun which is too powerful for the chassis.

"The Stryker's average weight of 17,100 kilograms -- along with other factors such as added equipment weight and less than ideal flight conditions -- significantly limits the C-130's flight range and reduces the size force that could be deployed," said a report from the Government Accountability Office, the investigative arm of Congress.

Friday's GAO report also said a C-130 carrying a Stryker would not be able to take off from all locations in higher elevations, such as Afghanistan, during daytime hours in summer.

The Stryker, an eight-wheeled armoured vehicle, is the U.S. army's first new combat vehicle in two decades. It was widely viewed as a visible symbol of efforts to transform the army into a faster, more agile fighting force. But critics have questioned its survivability and capabilities.

The army originally outlined operational requirements that sought to have a Stryker weigh 17,100 kilograms or less so it could be transported in a C-130 for up to 1,600 kilometres.

The report, however, said under ideal conditions with moderate air temperatures the C-130 would only be able to transport the Stryker for up to 1,385 kilometres. Add about 900 kilograms of equipment and ammunition and the flight range is cut to only 800 kilometres, the report said.

The army also initially wanted the Strykers to be ready for combat immediately upon unloading from the cargo plane onto the battlefield. The report challenged whether such a scenario would be possible because of the weight of the Strykers, plus additional gear and equipment.

Calls to the Pentagon for a response were not immediately returned.

But in its response to the GAO report, the U.S. Defence Department agreed: "Operational requirements for airlift capability for brigade transport need clarification."