Stronger-than-steel light combat trucks still a pipedream.

• Author: Erwin, Sandra I.

The U.S. military's dream truck undulates on and off roads like a Hummer, is transported via sling under a helicopter and, oh by the way, survives roadside bomb blasts.

Military truck buyers, alas, are recognizing that this is an impossible wish list. Even if it were technologically attainable, it would be financially unrealistic. Funds for new vehicles are expected to take a plunge in the coming years, and managers of the military's new Joint Light Tactical Vehicle are under strict orders to forgo costly bells and whistles and focus on what troops need most.

"Survivability is number one. Following is mobility," said Michael Halloran, director of science and technology at the Marine Corps' program executive office for land systems.

The JLTV program, intended for both the Army and the Marine Corps, is becoming a test case for how far military and industry engineers can push the boundaries of armor technology as they seek a truck to replace the Humvee later this decade. Halloran, who previously served as chief engineer for the mine-resistant ambush-protected (MRAP) vehicle, said the future truck ideally has to be nearly bomb proof like the MRAP but far lighter, more mobile and capable of going off road.

In JLTV, it's all about "tradeoffs," he said in an interview. "Do I need to make vehicles more survivable and give up mobility?"

It used to be that vehicle designers only were concerned with payload, performance and protection. Now cost has to be factored into the equation, said Halloran.

When the Defense Department first approved the JLTV procurement, there was a tacit belief that advanced new armor materials would be available to make trucks survivable without loading them with thousands of pounds of steel. But no breakthrough has emerged to slim down a 25,000-pound MRAP by 10,000 or more pounds.

"There is no novel lightweight armor material that has allowed us to achieve our weight savings," Halloran said.

"It comes down to physics. ... Anything under 30,000 pounds or 25,000 pounds has a tough time meeting survivability requirements," he said.

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Engineers have concluded that the way to drop vehicle weight without compromising the crew's protection is to take a comprehensive design approach that looks at how to make every piece of the vehicle more survivable.

"It's the seats, the floor, the V-shape hull. It's all those components and how you integrate those components to distribute the blast effects throughout the...