E-boat was the Western Allies' designation for the fast attack craft (German: Schnellboot, or S-Boot, meaning "fast boat") of the Kriegsmarine during World War II. The most popular, the S-100 class, were very seaworthy,[1] heavily armed and capable of sustaining 43.5 knots (80.6 km/h; 50.1 mph), briefly accelerating to 48 knots (89 km/h; 55 mph).[2]