The Land Mattress was an unfortunate moniker given to a fairly impressive experimental multiple rocket launcher developed by the US at the end of World War II. Developers began with the naval 5-inch shell, and mounted it on a 3-inch (76mm) rocket launcher mounted in a tube – the 60lb rocket or RP-3. It was actually first developed as a way to give cover to amphibious troops disembarking on a beachhead.
In 1944, when Allies were racing across Europe it was used. It could fire 4 rounds per second with arrange of over 7 kilometers. When Allies were crossing the Scheldt estuary over a thousand were fired on 6 hours.