The Department of Homeland Security’s (DHS) own watchdog says that drones deployed at the United States-Mexico border do not achieve their objective of protecting the country.

In a 37-page report issued on December 24, 2014 but published for the first time on Tuesday, DHS’ Office of the Inspector General (OIG) concluded that "after 8 years, [Customs and Border Protection, or CBP] cannot prove that the program is effective because it has not developed performance measures."

In a statement, the agency had a damning conclusion for the CBP drone program, which anticipates spending an additional $443 million to acquire and operate 14 more drones.

"Notwithstanding the significant investment, we see no evidence that the drones contribute to a more secure border, and there is no reason to invest additional taxpayer funds at this time," said Inspector General John Roth in the statement. "Securing our borders is a crucial mission for CBP and DHS. CBP’s drone program has so far fallen far short of being an asset to that effort."

Specifically, the OIG also noted that CBP’s estimated drone cost per hour ($2,468) is actually about 80 percent lower than the true cost ($12,555 per hour).

As the report states:

The Office of Air and Marine’s [OAM] calculation of $2,468 per flight hour does not include operating costs, such as the costs of pilots, equipment, and overhead. By not including all operating costs, CBP also cannot accurately assess the program’s cost effectiveness or make informed decisions about program expansion. In addition, unless CBP fully discloses all operating costs, Congress and the public are unaware of all the resources committed to the Unmanned Aircraft System program. As a result, CBP has invested significant funds in a program that has not achieved the expected results, and it cannot demonstrate how much the program has improved border security. Given the cost of the Unmanned Aircraft System program and its unproven effectiveness, CBP should reconsider its plan to expand the program. The $443 million that CBP plans to spend on program expansion could be put to better use by investing in alternatives, such as manned aircraft and ground surveillance assets.

In November 2014, the Associated Press, citing two anonymous sources from within the CBP, reported that drones now patrol over half of the US-Mexico border.

However, the new DHS OIG starkly disagrees with this assessment:

Although the Federal Aviation Administration permits OAM to fly over the southwest border from California to the Texas gulf coast, the unmanned aircraft focus on relatively small portions of the border. For example, according to CBP, in [fiscal year] 2013 UAS operations along the 1,993-mile southwest border focused on about 100 miles of Arizona border and operations in Texas concentrated on about 70 miles of that state’s border.

Brendan Schulman, one of the nation's few drone law experts, told Ars that he was not familiar with any other similar government drone-related studies.

"Smaller drones, used in closer proximity to border areas, may turn out to be far more efficient and effective at this type of mission," he wrote in an e-mail. "The Predator is a very large airframe that is over a decade old. One of the recommendations of the report is to conduct a study on whether investments in alternatives, such as manned aircraft and ground technologies, might work better. Newer, low-cost drones that have been developed over the past year or two might be another alternative worth investigating."