They will form part of NATO's enhanced forward presence (eFP), which was established to deter potential aggression from the Kremlin, during their three-month deployment.
Mr Williamson, speaking at the airfield, said: "It's a very credible threat that we see from Russia and part of the reason that we're deploying five Apache attack helicopters is making sure that we're constantly adapting to a changing situation, but this is about deterrents.
"This is about NATO nations standing together in unity as one and you see Great Britain playing the largest role in enhanced forward presence with the largest number of service personnel deployed.
"The enhancement of that deployment with the Apache attack helicopters is really vital and very, very important and it's been very warmly welcomed by so many nations."
The Apaches will be supported in Estonia by Wildcat battlefield reconnaissance helicopters.
A further 110 UK personnel have been deployed to the Baltics as part of Operation Cabrit, taking the total there to around 1,000.
Major David Lambert, commanding officer of 663 Squadron, 3 Regiment Army Air Corps, said the Apaches would take part in training exercises across the Baltic states while deployed to Estonia.
One of these, called Exercise Iron Wolf and taking part in Lithuania, will involve up to 14 nations.