The incidents, which occurred between Wednesday and Friday, saw "small unmanned aerial systems" spotted over RAF Lakenheath and RAF Mildenhall, in Suffolk, and RAF Feltwell in the neighbouring county of Norfolk.
The USAF, which uses the bases, said it was unclear at this stage whether the drones were considered hostile.
It also declined to comment on whether any defence mechanisms were used, but said it retained "the right to protect" installations.
A spokesperson for USAF in Europe said: "We can confirm that small unmanned aerial systems [UASs] were spotted in the vicinity of and over RAF Lakenheath, RAF Mildenhall and RAF Feltwell.
"The number of UASs fluctuated and they ranged in size/configuration.
"The UASs were actively monitored and installation leaders determined that none of the incursions impacted base residents or critical infrastructure.
"To protect operational security, we do not discuss our specific force protection measures but retain the right to protect the installation.
"We continue to monitor our airspace and are working with host-nation authorities and mission partners to ensure the safety of base personnel, facilities and assets."
MNA/
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