A record number of US military drones are mysteriously crashing from the sky and costing millions of dollars in damage. A total of 20 drones which are used for counterterrorism reconnaissance and airstrike missions were destroyed in 2015. Pentagon is reportedly keeping quiet on the cause behind the drones crashes and is failing to report all accidents despite being required to do so. The details of the crashes remain a secret.

Half of those involved the Air Force's latest and most advanced drones, the Reaper,  which suffered more than double an amount of crashes than any previous year. This is a cause of concern for the US military with each Reaper costing $14 million.

The Predator, an older version of its drone was involved in 10 major accident last year, the most  since 2011 when it was  heavily used in Afghanistan.

According to The Washington Post report, investigators believe the downed Reapers crashed due to electrical problems caused by a faulty starter-generator. They were even able to point out the three parts of the generator most prone to conking out. Problem is, they can't figure out why. It is not only the Reaper that is suddenly been falling out of the skies. The Predator has also been getting into accidents recently.

"Once the battery's gone, the airplane goes stupid and you lose it. Quite frankly, we don't have the root cause ironed out just yet," said Colonel Brandon Baker, chief of the Air Force's remotely piloted aircraft capabilities division.

Airforce Technology reported that a US Air Force drone crashed on 7 January 2016 in Central Iraq. The Air Force said in a statement that the Predator was not shot by the enemy missile but the remotely piloted aircraft collapsed when losing control of the aircraft. The specific cause of the crash still unknown but an investigation board will convene to determine it.

Meanwhile, the investigations are still underway, Defense One reported that Pentagon is thinking about higher-flying drones will be equipped with a laser. The laser is able to shoot down the ballistic missile.

It is for decades that Pentagon wants to bring the idea into reality. In the next three years, the laser technology will fit in on a high-altitude drone.

The drones can be designed to fly at 65.000 feet or higher, far above bad weather. They would stay at the height for weeks, hanging around launch sites so they could shoot upon enemy missile as they lift off.

Though a number of the accident on drones increase, the US Air Force continues to rely on drones to perform military duties. The Drones have become the Pentagon's favored weapon for conducting surveillance and airstrike for counterterrorism.