A submarine was filmed operating at periscope depth just off Gibraltar on July 11.
A local sports fisherman watched in amazement as a periscope emerged from the sea close to his vessel, slipping back beneath the surface a few moments later.
He filmed the submarine on two occasions that same day, both clearly inside British Gibraltar territorial waters off the east side of the Rock.
It is not clear whether the submarine in question was HMS Ambush, the British nuclear-powered submarine involved in a collision with a merchant vessel yesterday.
The Ministry of Defence has confirmed that HMS Ambush was submerged when it suffered a “glancing collision” with the ship.
The front of its conning tower was crushed by the blow but it sustained no damage to its nuclear power plant and there were no injuries.
The footage was filmed by Carlos Garcia, who said he and his friends were out at sea when they saw a helicopter dropping sonar buoys into the water while a frigate watched from a distance.
The MoD said yesterday that HMS Ambush had been involved in an exercise at the time of the collision.