Compressed air (submarines)

I'm not sure I understand your question. Submarines have compressed air banks that they use for emergencies. Buoyancy is maintained by pumping water into and out of the ballast tanks. They move water fore and aft to trim the boat and pump water in and out to maintain neutral buoyancy. In an emergency, they will open the "emergency blow" valves directing compressed air into the ballast tanks. This pushes out the water, reducing the overall weight and the submarine pops up to the surface. This is not normally done since this is an uncontrolled surface and there is a risk of the submarine hitting something.

Depth does affect the effectiveness of the emergency blow since it is harder to push out the water in the ballast tanks, but the air pressure is sufficient to handle that down to test depth.

Question comes about as I'm reading about Airships, they apparently share similarities, so I began looking at how compressed air is utilised aboard boats,
I had no idea for example its high pressure forces torpedo from tubes

Airships would be a more interesting question. On subs, air is used to push out water at high velocity. It could be in the ballast tanks or as you mentioned, a torpedo tube. (The large nuclear missiles are ejected using steam.) This wouldn't work on an airship. You need air lower in density than the surrounding atmosphere to get positive buoyancy (or a low density gas like Helium or Hydrogen). Compressing air makes it higher density, so not as effective. On the other hand, compressed air is a relatively light weight form of energy storage. It can also be pretty quiet. If you were writing a sci-fi or cyberpunk type novel with airships, if could think of some uses.