The Benares was a ship of unknown origin or class. She was most likely a merchant vessel.
When the merchant ship Karaboudjan sent out a false SOS message, the Benares, which was nearby to the Karaboudjan, immediately went to the aid of the ship. However, when it arrived, it found no survivors or wreckage, although it searched all night around the position given in the SOS signal. The Benares then assumed the Karaboudjan sank with all hands, and left the area. Unknown to the Benares, the Karaboudjan never sank, and simply wanted to fake her sinking so that she could disguise herself as the Djebel Amilah to avoid capture of the opium in her hold.
The Benares was only mentioned in a radio broadcast in The Crab with the Golden Claws and was never seen. She made no further appearances in the series.