Washington, D.C. ? The U.S. military is reinforcing the sides of its topline mine-resistant vehicles to shore up what could be weak points as troops see a spike in armor-piercing roadside bombings across Iraq, The Associated Press has learned.

The surge in attacks is putting the mine-resistant, ambush-protected vehicles (MRAPs) to the test, and so far they are largely passing. Statistics reviewed by the AP show that while bombings involving the deadly penetrating explosives have jumped by about 40 percent in the past three months, deaths in such bombings have dropped by as much as 17 percent.

Officials attribute much of the decline in deaths to the increased use of MRAPs, pronounced “M-raps.” To date, about a half-dozen troops have died in incidents that involved the new bomb-resistant vehicles, and several of those deaths occurred in rollovers rather than from explosives penetrating the armor.

Military officials spoke on condition of anonymity about the statistics because some are classified. Details of specific incidents often are not provided, making it difficult to determine which type of vehicle is involved in each roadside bombing.