There are no windows on the submarine. Underwater the water pressure would be too great, there would be little light and nothing really to look at. If the crew needed to ‘look around’ when they were submerged, then they would use sound waves, just like a dolphin would use echo-location to find a fish.
Sonar was a highly effective system of locating vessels in the local area. HMS Ocelot almost always ran in ‘passive’ mode, which was listening to what was around. While capable of transmitting, this was hardly ever used as it would give away the submarine’s presence and location.
Former Commanding Officer, Admiral Sir Trevor Soar, shares his thoughts on HMS OCELOT’s sonar system:
Walk around the grey building to find stop 6 on your left