A version of the Tu142 Bear has a trailing antenna that can be used to talk to submarines

One of the Russian aircraft that earlier this month flew along the west coast of Ireland with its transponder switched off is designed to communicate with submarines beneath the waves.

The Tu-142MR Bear-J was one of six aircraft monitored by Nato and European air forces in the space of a few days as it skirted the west coast before flying in circles off Kerry for two hours on March 7.

Military aviation experts say the aircraft is designed to communicate with submarines using a 5km-long trailing antenna, which it reels out in mid-air.

The aircraft was among six long-range Russian aircraft whose activities were monitored off the west coast on three separate occasions. The movements of the aircraft were tracked by Nato as they came