When the Defense Department began shipping a a new fleet of massive armored vehicles to Afghanistan in 2011, U.S. officials billed them as the Afghan National Army’s solution for rapidly sending troops into dangerous situations to reinforce fellow soldiers. The Mobile Strike Force Vehicles are based on the aging M117 armored personnel carrier that has been used since Vietnam, but with beefed up armor to defend against rocket-propelled grenades and other threats.

Most of the 634 strike force vehicles built for the Afghan army are now in its hands, according to a new audit report released Tuesday by the U.S.’s top watchdog on Afghan reconstruction. But the long-term outlook for the $661.3 million fleet of vehicles in the fight against the Taliban remains in question, the report says, citing deterioration in the vehicles due to a lack of spare parts and the patchwork nature of maintenance training.

The report comes as the U.S. and other coalition countries continue to withdraw troops across the country, limiting their reach as their combat role in Afghanistan comes to an end. The U.S. withdrawal calls for about 9,800 American troops in Afghanistan by the end of this year, with an additional 4,000 troops from other coalition countries. That’s down from a peak of more than 130,000 coalition troops in 2011.

The mobile strike vehicles were built by Textron Inc., of Providence, R.I. The report, by the Special Inspector General for Afghanistan Reconstruction’s (SIGAR) office, shows that Army officials reported that the company has performed well in providing the vehicles and the initial training to Afghan troops needed to use them. But Textron also is being paid as part of its contracts with the Defense Department to provide additional field training and maintenance, and it has not been able to do so because it is unable to reach the sites where the vehicles are kept, SIGAR found.

“According to NATO-Training Mission Afghanistan (NTM-A) officials, oversight personnel rarely conducted site inspections beyond Kabul, even though kandaks [Afghan battalions] are deployed to other provinces such as Zabul or Helmand,” SIGAR’s report said. “Although this provides for oversight of activities of in Kabul, it does not ensure that someone will provide oversight of Textron’s activities at MSF brigades and kandaks outside of Kabul.”

The U.S. Army Contracting Command agreed with some of the concerns raised by SIGAR, and pledged to provide more contractor support by the end of 2014. But the pledge came with a caveat — it will be “based on the amount of coalition security support” available, with the contract to Textron adjusted as required if security is not available.

A component of the International Security Assistance Force overseeing coalition operations in Afghanistan responded that it plans to consolidate mobile strike force depots in Kabul and Kandahar by the end of the year, making it easier to provide oversight.

SIGAR also found that while the Afghan troops assigned to mobile strike force units receive eight weeks of initial training, each crew member learned how to proficient in only one of three positions: driver, gunner, or vehicle commander. That leads to problems in some units if someone is wounded or deserts his unit.

“ANA soldiers selected to replace MSF crewmembers lost to attrition are often selected from infantry units and lack any MSFV experience. While the MSF brigade and kandaks in the Kabul vicinity can send individuals to the Armor Branch School, this is less feasible for the brigade and kandaks.”

Coalition military advisers with the mobile strike force unit in Helmand already have developed additional cross-training to make sure the Afghan troops can perform more than one job in their crew, SIGAR found. The watchdog recommended the development of additional follow-on training across the country, and coalition officials said it is coming.