MiG's.

This is coolbert:

From the War is Boring Internet web site thanks to the tip from Freeper an interesting article by Tom Cooper but not so totally complete:

"The Man Who Ruined the Soviet Warplane Industry"

"Meet Adolf Georgievich Tolkachev"

Tolkachev an agent of espionage for the Western power during the Cold War his damage to the Soviet warplane industry immense. Read it all.

In the proverbial nutshell:

"In the words of one Sukhoi engineer, 'it took more than 10,000 different upgrades and over 20 years' merely to improve the original Su-27 to the Su-27SM-standard, and thus 'repair some of the damage” Tolkachev caused.'"

"While full details on what exactly Tolkachev revealed to the CIA are unlikely to become public for a number of years, it was certainly a lot. The effects of his treachery — foremost the fact that an entire generation of brand-new combat aircraft, air-to-air and even surface-to-air missiles was compromised and thus became obsolete as soon as it entered service — are still being felt in Russia today."

EVEN BEFORE TOLKACHEV THE "SOVIET WARPLANE INDUSTRY" IN TROUBLE?

The MiG design bureau as it was called producing generations of warplanes that were inherently flawed, with intrinsic difficulties never it seems resolved!

MiG-21 in particular having a very bad reputation for crashing. THAT MOST-PRODUCED SUPERSONIC JET AIRCRAFT IN AVIATION HISTORY AND THE MOST-PRODUCED COMBAT AIRCRAFT SINCE THE KOREA WAR NOT QUITE AS RELIABLE AS BELIEVED, BECOMING UNCONDITIONALLY UNSTABLE WHEN 2/3 OF A FULL FUEL TANK EXPENDED!!

Now you know the rest of the story!

See some Strategy Page articles the topic of which the problems with a variety of MiG warplanes:

https://www.strategypage.com/htmw/htproc/articles/20091224.aspx

https://www.strategypage.com/htmw/htproc/20160423.aspx

https://www.strategypage.com/htmw/htairfo/articles/20160131.aspx

coolbert.