Fictional concealment and cruiser torpedo attacks

What if British cruisers received five twenty-minute invisibility devices apiece from 1939?

They could approach for surprise torpedo attacks or use concealment to outlast aircraft during withdrawal.

The scenario gives each British cruiser five devices that provide twenty minutes of invisibility to enemy observers and radar. That fictional capability would allow a cruiser to close for a torpedo attack before its opponent could respond. Bismarck and Graf Spee are used as examples of targets exposed to such an approach. Concealment could also help a cruiser withdraw under air attack once its ammunition was exhausted, exploiting the attacking aircraft's limited time on station.