ASROC is a
naval weapon system (
U.S. Navy designation RUM-139 for the
VLS version, RUR-5 for the
ABL version) that is deployed aboard U.S. Navy ships. It is an
ASW weapon, designed to allow surface ships to attack submerged targets without having to close to the range required for depth charges (which most modern U.S.
surface combatants don't carry anyhow).
There were four payload variants of the ASROC weapon. ASROC, by the way, is an acronym for Anti-Submarine ROCket. The first one was simple; the missile, upon leaving the ship, flew a ballistic trajectory to the designated target point and dropped a W-44 - based nuclear depth charge into the ocean. If the submarine wasn't vaporized (it wasn't a very big warhead) the shock waves from the detonation would crush it flat if it were anywhere in the area. This weapon was actually live-fired, once, in Operation SWORDFISH, a U.S. nuclear test performed in the Pacific. A truly fantastic surface column of water was displaced, producing a lightly-radioactive rain.
This effect was inspired by the Operation WIGWAM test, in which several submarine-like hulls were submerged 500 miles off San Diego, California and subjected to a nuclear explosion at approximately 2,000 feet of depth. The results were as expected.
In any case, the ASROC was not only designed for nuclear combat. The best weapon for fighting modern submarines is a torpedo, designed to hunt them in their own element. The problem facing surface ships is that torpedos don't have an extremely long endurance, and the act of dropping one into the water is extremely noisy. Thus, using them at long standoff range means that it's unlikely the torpedo will reach its target; if it can reach the target's position at launch, the target has the entire travel time of the torpedo to take evasive action. As modern torpedos (with some exceptions) travel only perhaps twice to three times the speed of a submerged submarine, running away to open the range is a quite effective maneuver.
In any case, the answer was found through a series redesign of the ASROC. In its conventional incarnation, the ASROC is designed to fly a tight ballistic arc and drop an antisubmarine torpedo into the water (a Mk. 44 or Mk. 46 lightweight version). This torpedo then chases the submarine. This is better because, if you have a fairly good idea where the submarine is, it's theoretically possible to have the ASROC drop the torpedo (pretty much) on the submarine's figurative noggin, leaving little time for fancy maneuvering or countermeasures. The two conventional variants (which are the only ones left today) carried these two torpedos, and contained fairly sophisticated guidance and nav gear - the torpedos aren't nearly as durable as a simple warhead, and needed to hit the water in a closely-prescribed manner in order to activate properly.
The final variant was a marriage of two worlds...an ASROC was modified to carry a Mk. 45 nuclear-tipped torpedo. While this may seem a bit of overkill...well, okay, it was. Even the U.S. Navy thought so, and it had a short life. This version dropped the torpedo in the air, and it was delivered to the surface by parachute.
In any case, the launch of the ASROC was initially done using the Armored Box Launchers found aboard most U.S. surface combatants of the 1950s through the 1970s. As the ships modernized, the box launchers fell by the wayside and a new version was introduced. This one sported a TLA - the VLA or Vertical Launch ASROC. Essentially it is the same conventional ASROC designed to launch from a vertical launch cell. The primary addition is that of more severe thrust vectoring on the booster, since the missile now needs to perform a complete 180-degree maneuver to hit the ocean if the target is too close for a ballistic delivery.
Our friends at the FAS offer the following specifications for the modern conventional VLA: