The Walter U-boat was designed to be very fast underwater, ca. 25 knots, for several hours. Once the hydrogen peroxide was gone it became a normal Diesel U-boat, a rather underpowered one at that. Navigating at 25 knots underwater is one thing, but fighting quite another, especially if your periscope starts vibrating at around 8 knots. Even if the Walter drive had been perfected, a rather tall order in itself, the boats were still vulnerable during the march since they originally had no snorkel and they would have their problems shooting accurately during the attack. My point is that a lot of R+D work needed to be done in periscope mounting and sonar in order for the Walter boats to fight effectively and they needed snorkels to get to the proximity of their targets. All this in addition to getting the drive to work.

The 70% hydrogen peroxide used as the oxidizer and partial heat source (the heat of decomposition is a significant part of the power produced) in the Walter drive is very dangerous and hard to handle, especially in the quantities we are discussing; 100 - 200 tons. There were already enough problems with the Me 163 and that used only several hundred kilos. No one ever got a Walter U-boat drive to run reliably, so this in combination with the hazards of hydrogen peroxide made the technology a dead end.

However, small scale use of the Water drive is another story. It worked in small rocket applications and as a torpedo drive. It may also have worked as a midget submarine drive, but carrying tens or hundreds of tons of hydrogen peroxide through a depth charge attack, no thank you. Someone in the Kriegsmarine did a lousy job of technology assessment on this subject. Walter should have learned to walk - torpedoes and minisubs - before he attempted to run. A reliable Walter drive torpedo would have caused quite some consternation in 1940; 40-45 knots and no wake.

Regards,
SuperKraut