The military is sending thousands of mine-resistant, ambush-protected vehicles to Afghanistan, even while a new version is being built, to protect troops against their biggest threat: improvised explosive devices. Because IEDs pose the biggest threat to troops in Afghanistan, the nation’s top military officer said yesterday, the military will keep the MRAPs flowing there until new versions built specifically for the Afghan terrain are ready for shipment. Navy Adm. Mike Mullen told a National Press Club audience that IEDs have become “more and more sophisticated over time.” Combined with increasingly sophisticated Taliban attacks, they pose an increasing threat to deployed troops, he said. Mullen offered his comments just before traveling to Dover Air Force Base, Del., as the remains of seven servicemembers -- six of them killed by roadside bombs -- were returned home from Afghanistan. While predicting casualties will continue to spike during tough fighting in the months ahead, Mullen said the Defense Department is flowing thousands of MRAPs into Afghanistan to protect forces there. So far, 3,020 MRAPs have been shipped to Afghanistan, reported Cynthia Bauer, a U.S. Transportation Command spokeswoman. That brings to more than 15,000 the number of MRAPs that Transcom has delivered to the theater, she said. About half of the Afghanistan deliveries were by airlift and half by “multi-modal” delivery, a combination of airlift and sealift. “From an equipment standpoint, there’s no higher priority than to get these vehicles in theater as rapidly as we can,” Mullen said yesterday.