Junead Khan used his job with a pharmaceutical firm to scout US bases for potential victims, a court heard.
The 25-year-old had driven past RAF (Royal Air Force) Lakenheath and discussed knifing a soldier.
Khan was also found guilty, along with his uncle, 23-year-old Shazib Khan, both of Bangladeshi origin, of preparing to go to Syria to join so-called Islamic State.
Shazib was given an extended sentence of 13 years in prison and will have to serve eight years in custody.
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Justice Edis said the two men had rejected the values and opportunities Britain gave them.
He said: "They both believe that Sharia law is the only legitimate law and both reject democracy, because it involves law being made by people and not by God.
"They have rejected the protection of the law of this country and education they have received by becoming committed supporters of ISIS - an organisation which wishes to control the world and which will stop short of no barbarity in order to do so."
His computer was found to contain an Al Qaeda bomb manual and Amazon searches for a large combat knife.