Two F-15 fighter jets carrying out 'high performance' manoeuvres were involved in a near-miss with a reconnaissance aircraft over Norfolk.
A report by the UK Airprox Board said the two US fighter jets turned towards a Boeing RC-135 on November 27 last year, despite receiving information about its location.
Radar data shows one F-15 came within 370m (1,214ft) of the RC-135.
The fighter jets executed a right-hand turn to avoid a crash.
The report said the F-15 pilots were given 'sufficient information' about the reconnaissance aircraft's location from a controller based in Swanwick, Hampshire.
However, it added they may not have fully understood it due to being involved in 'highly-dynamic manoeuvring'.
One jet was acting as an aggressor and the other as a defender, when they made a climbing left turn towards the reconnaissance aircraft.
While the F-15 pilots assessed the risk of collision as 'none', the RC-135 pilot believed it to be 'medium'.
The report said: 'The board agreed that the cause of the Airprox was that the F15 pilots flew into conflict with the RC135, despite having received traffic information.'
In regard to risk, it added: 'It was considered that although safety had been degraded, there had been no risk of a collision.'
It categorised the risk as C, the third highest level.
The United States operates F-15s from RAF Lakenheath and RC-135s from RAF Mildenhall in Suffolk.
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