The Pentagon will phase out its armored Humvees in Iraq and Afghanistan and send in vehicles that better withstand roadside bomb blasts, Defense Secretary Robert Gates said Wednesday.

Replacing the Humvee, the military's main troop-transport vehicle, will be the Mine Resistant Ambush Protected Vehicle, known as an MRAP. Military officials say the new vehicles provide twice as much protection against improvised explosive devices (IEDs), which cause 70% of all U.S. casualties in Iraq.

Armored Humvees were "the best we had," Gates said. "Now we have something better, and we're going to get that to the field as best we can."

No Marines had been killed in the 300 attacks on Marine MRAPs in Anbar province, USA TODAY reported on April 19. Last week, two Army soldiers were killed when a bomb struck their MRAP in Iraq.

Getting the MRAPs is "the highest priority Department of Defense acquisition program," Gates said in a memo last week to the secretaries of the Army and Navy. In that memo, first reported Wednesday by InsideDefense.com, Gates said he was concerned the Marines has ordered 3,700 of the vehicles, while the Army only sought 2,500. The Army has about 100,000 troops in Iraq; the Marines have 25,000.

Gates and other Pentagon officials plan to meet Friday to determine how many more vehicles the military will buy. "My understanding … is that the Army has been recalibrating its interest and has substantially increased the number of these vehicles they think they can use," Gates said.

The new vehicles feature a V-shaped hull that disperses explosions from below. All services have ordered a total of 7,700 MRAPs for $8 billion over the next 18 months, but Gates indicated the Pentagon could buy many more.

The Army now has 18,000 armored Humvees in Iraq. It originally planned to spend another $2.5 billion this year to buy more, Army budget records show.

Army spokesman Paul Boyce said Wednesday the service has 1,100 mine-protected vehicles in Iraq. The MRAP won't completely replace the Humvee in Iraq or future conflicts, he said.