HMS Nelson equipped with UP Launchers on her main turrets.
UP or "Unrotated Projectile" Launchers were 20 round rocket launchers designed to form a protective barrier against attacking aircraft. Rockets were fired 10 at a time.
the UP rockets were not direct fire weapons.
Once they reached a preset distance from the ship they would deploy a mine suspended from three parachutes via a length of wire. Aircraft that flew into the wires would detonate the mine. The idea was that that launchers could create an aerial minefield around the ship.
However, the minefield was rarely dense enough to provide an obstacle to attacking aircraft. In addition, the slightest wind could disperse the mines over a wide area, even onto friendly ships and even back onto the ship that launched them. Last but not least, the supply of rockets stashed aboard a ship posed a significant fire hazard. During her final battle, HMS Hood took a hit on her boat deck that ignited her UP rockets, causing a large fire.
Though an interesting concept, the weapon was largely ineffective and quickly removed from British ships in 1941 in favor of additional AA guns.
"These things must be done delicately-- or you hurt the spell." - The Wicked Witch of the West.
"We've got the torpedo damage temporarily shored up, the fires out and soon will have the ship back on an even keel. But I would suggest, sir, that if you have to take any more torpedoes, you take 'em on the starboard side." Pops Healy, DCA USS Lexington.