After a ten-day work-up on-board HMS Illustrious around the Cornish coast, the Merlin Carrier Air Group (MCAG) prepare to “go deep” as they sail westwards out into the Atlantic in pursuit of submarines.

Illustrious anchored off Pendennis Point last week to embark helicopters before exercising off the coast.

Exercise Deep Blue has so far seen the Merlin Mk 2s from Royal Naval Air Station Culdrose being put through their paces in the South West Approaches, exercising and practicing before they get a sniff at a live target.

That will come as they move westwards where they expect to find UK and Dutch submarines trying to penetrate a tight anti-submarine shield around HMS Illustrious and the two Type 23 frigates who are joining the task group for the exercise.

“We have nine Merlin Mk 2s onboard,” said Commander Ross Spooner, commanding officer of 820 NAS and commander of the MCAG. “What we anticipate to deliver throughout this exercise is protection for the fleet. Three aircraft will be in the air at any one time, two of them on station 24 hours a day.”

The role of the Merlins is to keep the submarines away from the carrier. High tech sonobouys are dropped in the water at intervals to form a barrier or screen to detect the enemy.

The aircraft also has a dipping sonar to “ping” a signal out and listen to returns should an adversary get near to the task group. Torpedoes and depth charges can then be deployed to persecute and destroy the targets.

Aircrews and engineers work to punishing schedules to keep the momentum up. Pilots, observers and aircrew work a “sleep, eat, fly, sleep” rotation, constantly planning the next stage of the routine, with little concept of the 24-hour clock.