The submarine operates at three levels.

On the surface she is like a surface ship, easy to see and very vulnerable to shot, shell and missile.

At periscope depth she is much more discreet and difficult to see except at very short range. She can still run her diesels, using the snort mast.

S99 underway on the surface.

Deep dived she is in her element, moving silently below the temperature layers and almost impossible to detect. She can remain dived on battery power for up to five days at a time.

Using her passive sonars she is able to hear, track and to sink ships 10 kilometres away by using torpedoes.

S99 alongside, the forward passive sonar housing bulge clearly visible

External Torpedo Tubes

There are four External Torpedo Tubes situated aft of the fin, outside the pressure hull. The Midships group are offset to 8.5 degrees to the centre-line of the submarine.

Three of the submarine's external Torpedo Tubes clearly visible as the ferry approaches to drop off visitors.
(Photo by: Robert A (BOB) Johnston)


  • Length 4.470m

  • Inside diameter 553mm