Editing Venona project (section)

=== Black Friday === 

In late October 1948 the Soviets began changing their ciphers one by one in rapid succession. They also stopped the use of UHF radio links from Germany and Austria to Moscow, using (overhead) landline instead. While Navy investigators thought it was a routine systems upgrade others were not so sure and later it was attributed to two Soviet spies: American William (Bill) [[Bill Weisband|Weisband]], a linguist at Arlington Hall and British [[Kim Philby]] in the SIS.{{sfn|Vogel|2019|pp=15-17 }} 

At this time some  information was trickling in from US intercepts and rare overflights near the East-West border; but with a dearth in intelligence, not even a hint was received of the North Korean attack (approved by Stalin) on South Korea in June 1950. This led to the approval of [[Operation Gold]] in Berlin, a joint CIA/SIS operation to tap into underground telephone cables a short distance across the border in East Berlin; the scheme was based on [[Operation Silver (1949)|Operation Silver]] a British SIS operation in Vienna.{{sfn|Vogel|2019|pp=}}  

Operation Gold was betrayed to the NKVD/KGB by British SIS member [[George Blake]] even before it started intercepting in May 1955. But to avoid compromising Blake, it was allowed to continue to April 1956, with knowledge of the project kept inside the organisation.{{sfn|Vogel|2019|pp= 227,280 }}