The Defense Department will start sending M-ATVs to Afghanistan by ship “sometime after the first of the year,” said Cynthia Bauer, of U.S. Transportation Command.

Until then, the vehicles will be flown into Afghanistan, limiting how many can be sent.

M-ATVs are 25,000-pound versions of MRAPs that are designed to go off road. They were designed specifically for Afghanistan, which doesn’t have a well developed road network. As of Tuesday, 41 M-ATVs had been flown to Afghanistan, said Defense Department spokeswoman Cheryl Irwin.

The Defense Department has received about 700 vehicles so far, of which 400 were delivered in October, said Marine Corps Brig. Gen. Michael Brogan, who oversees the M-ATV acquisition program.

Before they are shipped downrange, the M-ATVs have to be fitted with radios, jammers and other gear in Charleston, S.C. The process takes about five hours, Brogan said on Monday.

The Defense Department has authorized 6,644 vehicles for all of the services.

Oshkosh Corp., the only company building M-ATVs for the Defense Department, plans to build 664 vehicles in November and 1,000 per month beginning in December, said Kenneth Juergens, senior program director for the M-ATV for Oshkosh Defense.