A Royal Navy sailor has been arrested after entering an officer's cabin on board a warship with a loaded weapon, the Ministry of Defence has confirmed.
The incident happened on the Type 42 destroyer HMS Edinburgh while off the coast of Portugal on September 28.
The rating was detained after entering the executive officer's cabin and has been brought back to the UK while service police investigate the incident.
An MoD spokesman said: "The Royal Navy can confirm that a rating from HMS Edinburgh was arrested following an incident on September 28 and the rating was returned to the UK.
"The incident is still under investigation and no charges have been made; therefore it would be inappropriate to comment further."
The incident follows concerns being raised by Portsmouth Coroner David Horsley over the security of firearms on Royal Navy warships.
Following an inquest in August into the death of 20-year-old Engineering Technician Samuel Hatton, who shot himself on board HMS Cattistock with a ship's rifle, Mr Horsley said he would write to the Navy,. calling on it to increase security for weapons storage.
In another incident, an officer was killed and another injured in a shooting on submarine HMS Astute in Southampton in April 2011.
Able Seaman Ryan Donovan was jailed for at least 25 years for murder at Winchester Crown Court in September 2011.