The military was called in to assist Heathrow last night (8 January) after departures at the West London airport were put on shutdown for around an hour following another drone sighting.
The military and police suggested that top secret equipment was used to hunt for the drone and would not go into details about the technology or tactics used.
Flights from the airport resumed about an hour after police said a drone had been seen, however concern was running high following the prolonged shut down at Gatwick weeks before, which saw thousands of people stranded.
Heathrow said it was 'working closely with the Met Police to prevent any threat to operational safety'.
Temporarily preventing flight departures was a 'a precautionary measure' a spokesperson said.
Metropolitan Police Commander Stuart Cundy confirmed military assistance had been brought in.
A Ministry of Defence spokesman said it deployed 'specialist equipment to Heathrow Airport at the request of the Metropolitan Police'.
Commander Cundy said: 'Police officers were amongst those who saw the drone and a full criminal investigation has been launched. We are carrying out extensive searches around the Heathrow area to identify any people who may be responsible for the operation of the drone.
'We are deploying significant resources - both in terms of officers and equipment - to monitor the airspace around Heathrow and to quickly detect and disrupt any illegal drone activity; some of which are as a result of learning from the incidents at Gatwick.
'Following today's sighting, military assistance has been implemented to support us. However, we will not be discussing in any further detail the range of tactics available to us as this would only serve to potentially undermine their effectiveness.'