The U.S. military heavy armored anti-bombing vehicle failed to meet its requirements on Saturday, as one soldier was killed and three were injured after a buried bomb went off when the Mine Resistant Ambush Protected vehicle ran over it and caused the vehicle to roll over. The incident took place in the southern part of Baghdad, near Arab Jabour, U.S. officials said on Tuesday.

The Mine Resistant Ambush Protected vehicle was designed especially to protect its passengers from roadside bomb, and the Defense Secretary Robert Gates considered bringing them to Iraq a top priority. Investigators are trying to uncover the cause of death and answer the rumors that say it might have had a flaw in design.

According to investigators on the scene, the soldier killed was the most exposed to either the blast or the overturn of the car, while the lives of the other three were most certainly saved by the MRAP vehicle, how it is known. Apparently the blast was very strong and the impact on the vehicle was a violent one; the good part is there has only been one victim instead of four.

This is the first incident that ends up with a dead soldier ever since the vehicle was introduced to the Iraq operations. It has done its job so far, but like officials said, no vehicle is perfect. Moreover, the soldier killed in the blast was the gunner, who was also the most exposed, and if the blast didn’t kill him, the overturn of the car would have.

The $12 million project was meant to replace the use of Humvees with vehicles that increase the safety of its passengers, especially with the high number of roadside bombs that endangered the lives of the U.S. soldiers in Iraq. The military plans to double the number of MRAPs up to 15,000 which would cost them around $22 million, but the investment is definitely worth it, officials say.