This is why the SAS Blue Thunder helicopter is flying over Yorkshire today

A helicopter used by elite Special Forces that can be deployed at a 'moment's notice' was seen over West Yorkshire today.

Blue Thunder landing on London Bridge in 2017

The SAS aircraft is nicknamed 'Blue Thunder' and can be dispatched to an emergency situation on the direct orders of the Home Secretary.

Blue Thunder is deployed to London Bridge terror attacksThe unmarked helicopter was pictured above Dewsbury just before midday and was flying with its transponders switched off, meaning it does not appear on radar or flight tracking apps.

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The chopper is believed to be in West Yorkshire on a training exercise in the Ferrybridge area. It is navy blue with a white undercarriage.

In November, the Ferrybridge power station site was used for a 12-hour counter-terrorism training exercise involving staged explosions, gunfire, and a simulated hostage situation.In June 2017, Blue Thunder was deployed on the UK's streets for the first time when it landed near London Bridge following a terror attack.

The 70-strong Special Forces squad was formed in 2015 specifically in response to the threat from 'lone wolf' attackers, and they rehearse such scenarios regularly. News of the unit's formation emerged after the Brussels terror attacks, and they are now on standby around the clock. Their deployments are supported by an Apache gunship helicopter.

Did you take any photos of Blue Thunder over Yorkshire? Email [email protected] and we will use them with a credit.