These 10 military aircraft were meant to be kept secret but ended up being revealed to the public through leaked information.

Developing a new aircraft for the military is an immense undertaking. As some of the ultimate machines, aircraft require intense engineering for every minor part, and as a cohesive unit can take several do-overs to get right. If said aircraft is public knowledge, this isn't the biggest deal, as test flights, and any developments can be conducted and announced on demand.

But, in the world of classified military projects, the development of new aircraft is made even more intense thanks to the veil of secrecy required at each step of the way. Whether it's for stealth technology, or a new weapons system, secret aircraft are desperately kept a secret to stay ahead of the competition and keep their new developments out of enemy hands.

Things don't always go to plan though. Over the course of secret military aircraft development, information can get out through leaks, whether deliberately staged or not. Sometimes a necessary distraction from true intentions and other times a complete fluke that was never meant to happen, these 10 military aircraft were meant to be kept secret, but ended up being revealed to the public through leaked information:

10 Lockheed YF-12

Few aircraft are as emblematic of classified secret projects like the SR-71 Blackbird and its CIA brother, the A-12. As the ultimate spy plane, Blackbird development and operations were a massive endeavor, with the utmost care put into keeping things under wraps.

With the development of the A-12 reaching its final stages in 1962, fears of the aircraft being revealed to the public during test flights were a major concern, as one incident could undo years of secrecy.

Rather than risk the aircraft being revealed through conditions out of CIA and government control, the White House announced the existence of an ultra-fast experimental aircraft in 1964 and leaked information on the armed YF-12 interceptor prototype - omitting any mention of its role in developing the SR-71 and A-12 spy planes. This acted as a distraction from the SR-71 and A-12's true purpose and scale of production, helping to maintain the spy plane's secrecy for decades.

9 Lockheed RQ-170 Sentinel

While stories of secret aircraft projects like the SR-71 seem like they could never happen today in the age of instant communications and global connectivity, that isn't the full truth, and projects like the RQ-170 continue the game of secret spy plane development.

Designed and made by the Lockheed Skunk Works (the same team responsible for the SR-71), the RQ-170 Sentinel is a classified stealth surveillance drone. While specific details are still a US government secret, the RQ-170 was unceremoniously brought to public light in 2011, when one crashed in Iran, subsequently being captured by the Iranian military, reverse engineered, and shown to the world.

8 Sukhoi S-70 Okhotnik-B

A Russian stealth drone along the lines of the RQ-170, the Okhotnik (Russian for "Hunter") is part of the latest generation of secretive drone development.

While recently, a video was released by Russia showing the drone taking its first flight, the first true glimpse of the Okhotnik-B came in the form of leaked photos. Developed in secrecy starting in 2011, the Okhotnik-B's true form was revealed when pictures were posted to Russian social media in 2019 showing the mysterious aircraft being towed at an air force base Russian President Vladimir Putin was visiting.

7 Hongdu GJ-11 Sharp Sword

It has become evident in the last decade that advanced, stealth and combat-capable drones are quickly taking over as the future of air combat operations, and the focus of intense development by world powers.

With its own wave of advanced aircraft development underway, China looked to this technology for future development. Naturally, the leading edge of stealth developments are kept a secret, but images of the Sharp Sword drone were leaked to the internet in 2013 (pictured above), showing the mysterious aircraft's form. 6 years later, and the GL-11 Sharp Sword was shown in full display to the public during the 2019 Beijing military parade.

6 Sikorsky Stealth Black Hawk

A long-serving workhorse helicopter, the Sikorsky UH-60 Black Hawk is a legendary aircraft that's been reliably transporting military personnel since the '70s.

But, looking forward to future advancements, the US military and Sikorsky have had plans to create a stealth capable version since 1978. No official word on a stealth Black Hawk's existence has been given, but, during the 2011 raid that was responsible for killing Osama Bin Laden, a Black Hawk crashed, and revealed something interesting.

The wreckage was destroyed with explosives by special forces, but the tail section remained and was found to be unlike anything confirmed to exist in America's arsenal. With photos of the tail section leaked (pictured above), connections were made to the previous plans and concepts for a stealth Black Hawk and were furthered by yet another leaked photo (first in this entry) that showed a mysterious, stealthy looking Black Hawk up close.

5 Mikoyan Gurevich MIG-25 Foxbat

Developed in secrecy, and focused on countering the increasingly rapid threat of American bombers and spy planes, the Soviet MIG-25 was among the fastest jet aircraft to ever fly.

While the USA managed to obtain photos and knowledge of the MIG-25's existence, the information was vastly incomplete, shrouding the MIG-25 in mystery about its full capabilities and true purpose.

But, a lucky break came in 1976, when Soviet pilot Victor Belenko stole one of the secretive interceptors, and defected with it, offering the aircraft in exchange for asylum in America. Landing in Japan, the unexpected arrival brought much attention. Rushing to see the mysterious aircraft, close up pictures of the MIG-25 were taken by reporters, and leaked to the public. As well, the USA was able to fully dismantle and study the jet, solving the mystery of the MIG-25's capabilities and purpose.

4 Chengdu J-20 Mighty Dragon

China's entry to the modern, ultra-advanced fifth generation of fighter jets, the Chengdu J20 is a stealth fighter jet developed in similar secrecy.

Intended to help the Chinese air force (PLAAF) catch up with ultra-advanced stealth capable fighters like the F-22, the J20 is equipped with plenty of advanced technology like stealth, precision targeting, and immense speed.

While initial phases of development were kept in the dark, come 2011, full pictures of the J20 were suddenly leaked to Chinese message boards and newspapers. With no effort by the Chinese state to censor or prevent the photos from spreading, it's theorized that the leaks were intentional to debut and show off the aircraft, but regardless, were the first looks the world got at the new fighter.

3 Lockheed F-117 Nighthawk

The origins of stealth combat aircraft, the F-117 Nighthawk is an iconic bomber that was developed in secrecy by the Lockheed Skunk Works.

Starting in 1977, the experimental Have Blue stealth concept conducted test flights, developing into the F-117 which first took flight in 1981. But, such a radical-looking aircraft with secret new technology was a struggle to conceal fully, and a stream of leaks gave the public insight into the aircraft.

In 1982, a Washington Post article disclosed developments into stealth aircraft, and then in 1986 an F-117 crashed during testing, an incident also covered by the Washington Post. Unable to keep the secret fully, the Pentagon deliberately leaked a photo of the aircraft in 1988, then fully de-classified and showed the F-117 to the public in 1990.

2 Northrop Grumman B-21 Raider

Still shrouded in secrecy, the B-21 Raider has been subject to intense speculation ever since officially mentioned in 2016, fueling rumors around the nature of the new bomber.

With details still highly classified, the B-21 Raider is on track to be a replacement for the USAF's current bomber fleet, including the Northrop Grumman built B-2 stealth bomber.

In 2016, the picture of the B-21 above was released showing the basic form of the B-21. This year, a more detailed rendering of the aircraft was released by Northrop Grumman (top picture of this entry). While details are slow to emerge, Northrop Grumman's leak of the B-21's true form came without US air force comment or explanation and is the closest and most detailed look the public has received into the future of American stealth bombers.

1 Bell P-59 Airacomet

America's first fighter jet, the Bell P-59 was designed and developed in secrecy during WWII with hopes of putting the USA ahead of the curve, and straight into the jet age.

With Germany having entered the world's first fighter jet into service, and Britain not far behind, an American fighter jet was urgently needed. While a technology that is common knowledge today, jet engines were a classified development during WWII that remained mostly unknown to the public.

Developing the XP-59 prototype in secret, a problem arose when shipping the aircraft. If the public caught sight of the radical propeller-less plane, the secret jet engine developments could get out, so the prototype was hidden in plain sight. Transported in the open, the P-59 was fitted with a fake propeller, revealing its form to the public, while maintaining the secrecy of its new jet engines.

(Source: https://www.hotcars.com/secret-military-aircraft-that-were-leaked-to-the-public/)