More than 4,000 gardaí and 2,000 members of the Defence Forces surrounded the airport and the castle, eight miles apart, as Air Force One touched down.
Security chiefs earlier yesterday activated the €3 million protection plan, which involves the deployment of Army surface-to-air missiles and hi-tech satellite communications.
Defence Force teams trained to deal with chemical or biological bomb attacks are on call while extra bomb disposal teams are on stand-by.
Gardaí have primary responsibility for the president’s security during his 18 hours in Clare, with Assistant Commissioner Dermot Jennings of the Western Region in command.
The heavily armed Garda Emergency Response Unit, the Army’s crack Ranger Wing and US Secret Service agents have key roles in protecting US President George W Bush.
Gardaí are also providing armed protection for US Secretary of State Colin Powell, National Security Adviser Condoleezza Rice and secretary of state for commerce Donald Evans, as well as for EU Commission president Romano Prodi and Taoiseach Bertie Ahern.
Four Naval Service ships patrolled the Shannon Estuary and the coastline while Air Corps helicopters and planes are providing aerial support.
The Mid Western Health Board (MWHB) has designated hospitals in Ennis and Limerick to receive casualties from any possible incidents. Plans have also been made for additional beds while extra medical and nursing staff will be on call.
A chemical decontamination unit has been set up by the MWHB beside a special medical centre at Shannon Airport to deal with people suffering any minor injuries.
Temporary CCTV cameras have been erected at the proposed protest sites. Garda Air Support will supply video footage of all activities. Three Garda command centres have been sited at Shannon Airport, Dromoland Castle and Shannon Garda Station.
Gardaí have received two water cannons from the Police Service of Northern Ireland (PSNI). These are on stand-by in Shannon.
Special arrangements have been made for the detention of prisoners in Limerick Prison. A unit in Shannon Industrial Estate has been designated as a garda station-courthouse and detention centre to ensure the smooth and timely processing of prisoners.