James Lybrand - Collins class: A true submarine
The ocean is broken down into various layers and i general, there's basically a warmer layer at the surface, where it's the same temperature basically called an isothermal layer, then it will generally break to a negative temperature grade, so decrease in temperature. And then at some later stage, that'll sort of slowly increase in temperature as well.
And by using various layers of the ocean, you can detect in layer or out of layer passive transmissions or active transmissions and, of course, it's better to transit, probably not, of course, but it's better to transit deep because the way the propeller operates, if you operate the propeller above certain revolutions, or put it on too fast to surface, you'll get what's called cavitation on the blade tips, which is an immediate identifier of a submarine if you're deep and it's inefficient for the propeller to do so.
So you would go deep and actually transit deep and often you can do that in hot water because it's cooler down below you actually cooled the submarine down by, in an Oberon you would open the main ballast tank vent valves and water would actually flow through those tanks and, important to note I guess to my earlier point, that an Oberon was a cylinder, a steel cylinder that had tanks on the outside of it basically which allowed you to dive and surface the ballast tanks, there are also some oil and fuel tanks there as well but a Collins is a steel cylinder that has all the ballast tanks internal to it.
So you've got, you know, effectively, you know, a couple of inches to sort of, inch and, I think, three quarters steel as the outside of the hull with anechoic tiling around it, which is what makes it that pure submarine verse, effectively a submersible or a part time submersible.