A newly uncovered report by the Defense Department’s own top watchdog says the Army and Air Force may have squandered more than $500 million to develop the same unmanned drone aircraft.

A 2010 Pentagon Inspector General report, obtained by The Intercept through a Freedom of Information Act request, says the services spent $115 million between 2008 and 2009 on research efforts to combine their Predator drone programs that ultimately proved “ineffective.”

The failure robbed DOD of an estimated $400 million in savings that would have been produced by a shared program, according to the IG study.

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The report lays bare the differences in how the two military branches approached their drone programs and how they employed them. While the Air Force staked itself as the leader for such efforts, the Army was purchasing its own Predator platform known as Sky Warrior.

In 2008, Pentagon leaders ordered the Army and Air Force to combine their programs in a bid to save money, as they were essentially buying the same kind of drone from General Atomics Aeronautical Systems, though the aircraft differed in certain ways, such as the fuel they used.

But the services never acted on the order. The Air Force stopped buying the Predator, opting for its larger variant, the Reaper, which still flies in several versions in combat zones today.

The Pentagon plans to buy 29 Reapers in fiscal year 2016 at a cost of $821 million, up from 24 in 2015 and 20 in 2014. The drones cost about $14 million apiece.

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The increase isn’t surprising, given President Obama’s reliance on drones to conduct airstrikes against Islamic State forces in Iraq and Syria and against other high-priority terror targets in other countries in the region, like Yemen.

The Reaper is also used by Britain, France and Italy, and has been ordered by the Netherlands.