Thanks to Jeff Dodge for the article below which describes on-going efforts at Penn State involving development of a bubble-screen system that would permit full-scale submarines to achieve extremely high speeds.

The article discusses Soviet development of a supercavitating rocket torpedo, the Shkval which could achieve speeds of 200 knots for very brief periods.

The article acknowledges that operation of a full-scale submarine in a supercavitating mode would create high levels of noise. What the article does not acknowledge is that the noise levels probably would permit detection at trans-oceanic ranges.

ARTICLE

"Supercavitation" Could Let Submarines Move Ridiculously Fast

Kyle Mizokami June 29, 2016

From Popular Mechanics

Researchers at Penn State are working to enclose the submarines of the future in a bubble of gas, allowing them to achieve top speeds faster than what is possible while moving through regular water. If successful, it could mean submarines capable of speeds of up to hundreds of miles per hour.

As submarines and torpedoes travel through seawater they are naturally at the mercy of physics, and objects traveling through sea travel encounter much more drag than objects traveling through air. The end result is that the practical speed limit of submarines is somewhere around 30 to 40 knots. Even with nuclear propulsion, that's about the best many military submarines can do.

But what if it were possible to enclose a submarine in a gas as it travels through liquid? That's the principle behind supercavitation.

There is a precedent: the Russian VA-111 Shkval torpedo. Developed in the 1970s, Shkval is equipped with a bubble generator in the nose that envelops the torpedo in a gas membrane while a solid rocket fuel engine provides thrust. The Shkval is capable of speeds in excess of 200 knots-up to five times faster than conventional torpedoes.

Scientists at Penn State are currently trying to understand so-called "pulsation"-the continuous cycle of shrinkage and expansion of a gas bubble around an object that occurs during supercavitation. Pulsation creates an inconsistent bubble unsuitable for travel, but before they can tame pulsation, the scientists need to understand how it works. Pulsation is difficult to create under laboratory conditions, but researchers at Penn State have managed to pull it off.
Supercavitating submarines wouldn't be perfect. Ultimately submarines are stealthy killers, relying on their ability to remain undetected. Maintaining a giant gas bubble would be very noisy, making the submarine easy to locate. A compromise might be a submarine that can sprint from its base at, say San Diego by supercavitation, and then switch to slow-and-stealthy mode once it gets to a patrol zone in the western Pacific.

Another thing about supercavitating submarines: if they, like Shkval, used rocket motors for thrust the subs would generate tremendous amounts of pollution, dumping rocket exhaust directly into the oceans. Not the most eco-friendly propulsion system, but seriously impressive if it can be made to work.