The 1945 German Type XXI U-boats were the first true submarines able to stay down at 300+ meters for long periods of time instead of running on the surface and being a mere submersible. The Type XXI was stealth-coated with a rubber substance called Opanol and the Schnorkel was also masked by Tarnmatte. All instrumentation and optics that protruded from the conning tower were retractable and the U-boat was protected by 4x 30mm cannons in AA role. It had a diving plane and lethal wire-guided torpedos (in addtion to homing types and zig-zag types) fed by an autoloader. It had silent V-belt drive and huge battery space. Also had a fully stocked galley with refrigeration and was spacious compared to the older Type VIIC. Two went out on patrol but were ordered not to sink any ships due to impending German surrender. Both carried out mock-attacks against both warships and convoys- undetected. Post-war various navies used captured Type XXIs to improve their subs drastically. The US, USSR, France, and Britain all had them and W Germany used one to restart its U-boat small numbers. Although this was the last official U-boat Type to get into the water, the Germans also planned to use the Type XVIII with AIP propulsion system and more lethal Type XXVI of which 4 were laid-down. Hundreds of Type XXIs were under construction (final assembly as the sections were pre-fabricated) when the war ended.

*Type XXIs and XXIIIs had Opanol rubber coating to absorb sonar and also had the Schnokel stealth-masked with Tarnmatte for surface running. Aircraft stealth was derived from Kriegsmarine stealth- the Hortens used similar RAM for the Ho-IX stealth jet fighter in Feb 1945 (the V3 captured by the US).