Vertical Launch System (VLS) - an arrangement for launching guided missile weapons vertically from a prepackaged canister. This maximizes both weapon storage space and availability as well as minimizing complexity - the launch system is open to the sky, meaning that the weapons need not be moved or aligned prior to launch, relying instead on their onboard guidance to align them once they have left the launch system. Typically, these systems are used aboard naval vessels, where space is tightly constrained and complex systems (such as moving launchers or reloading rails) are difficult to maintain.

The U.S. Navy's current VLS system is the Mark 41 VLS. It consists of several components, including the launch tubes (called 'cells') which come in blocks of eight (2x4); a remote control console, and a status indicator panel, both of which are mounted elsewhere inside the ship. In addition, there are control computers for the system. Additional eight-cell modules can be added to the base system to produce installations with greater magazine size; at least one must be a 'system module' which contains the control systems for the cells. In addition, a special module can be installed of which four cells have been removed in favor of a built-in crane, allowing the ship to lift and load its own replacement canisters into the cells from alongside without requiring a ship or dock with a crane of its own. The crane cannot, however, handle all types of canister - the Standard SM-2 Block IV and the Tomahawk TLAM canisters are too heavy to be reloaded at sea using the built-in crane and must be reloaded in port.

There are two types of Mk. 41, differentiated by the length (or depth, depending on how you look at it) of the launching tubes. The VLS Strike can take the longest available canisters, allowing for longer (and hence longer range and greater payload) weapons. The VLS Tactical is shorter.

Various different types of missiles can and are mixed into the loadout of a ship's VLS, including strike and SSD (ship self defense) loads. At present, the U.S. Mk. 41 can be loaded with any of the following types of canister:

  • Sea Sparrow - Ship Self Defense, SAM. Single missile per canister. Used against aircraft and cruise missiles. Short range, radar-guided.
  • Standard SM-2 Block II - Ship Self Defense, SAM. Single missile per canister. Used against aircraft and cruise missiles. Medium range, radar-guided.
  • VL-ASROC - Ship Self Defense, ASW. Vertical Launch variant of the ASROC (Anti-Submarine ROCket). Single weapon per canister.
  • Tomahawk TLAM - Strike, SLCM. Conventional land-attack cruise missile. Single weapon per canister.
  • Standard SM-2 Block IV/IVa (SM-2 ER Extended Range) - Ship Self Defense, SAM/ABM. Single missile per canister. Used against aircraft, cruise missiles and theater ballistic missiles. Long range, radar-guided.

There are additional canisters in development or early deployment, including those carrying navalised versions of the Army ATACMS missile as well as single and dual-missile canisters for the Navy's Land-attack Standard Missile. There is an Evolved Sea Sparrow (ESSM) canister quad missile canister which, in addition to being loadable in Mk. 41 VLS systems, may be usable in angled rail launchers as 'single-shot' self-defense weapons for smaller ships which do not have VLS.

VLS systems differ from the classic 'missile tube' aboard an SSBN or SSGN in that rather than each missile tube containing a full set of control systems and being essentially an independent system, along with having separate ejection charges for underwater launch, the VLS is deliberately designed as a modular system with reloadable cells for use in a variety of installed spaces.

Other nations have their own versions of VLS, of course! Russian yards have been installing VLS systems to launch SAMs and cruise missiles for at least as long, if not longer, than the U.S. Both nations will happily sell VLS systems to allies and nonaligned customers, and they can be found on ships of all nations. They're not only limited to surface vessels; the U.S. SSN 688 Los Angeles flight II and later boats have VLS tubes in the bow to allow them to launch Tomahawk cruise missile salvos without having to use the torpedo tubes.

Transitional Man brings up some excellent points about the comparative advantages and disadvantages of the VLS system. On the plus side, using prepackaged rounds in deck-accessible slots which serve for both storage and launch means that there is no need to maneuver large, heavy, fragile and dangerous objects through the interior of the ship into magazines. This eliminates the requirements for passageways for both onloading the rounds during resupply, and for sending rounds to launchers during combat - as well as eliminating the need for large and complex mechanisms to move the rounds at speed. Saving space, weight, power requirements and complexity on board a warship are always good things; each savings allows other systems to be put aboard to either increase the fighting capability of the ship or to increase its resiliency under fire and underway. Better damage control, better compartmentalization, more redundant systems, more living space - all will pay dividends of one form or another.

There are, of course, disadvantages as well. TM's initial message to me emphasizes one of them - despite the addition of onboard cranes for canister handling, reloading a VLS system at sea is much more difficult than reloading a traditional magazine. This is because while ammunition for a traditional ship need only be transferred horizontally before being immediately locked to a rail system for transfer into the magazine, a VLS canister must be raised vertically above the deck so that it can be lowered into its slot. This is suboptimal on a ship at sea, which will be rolling around an axis somewhere near its waterline! As a result, the canister and its handling equipment will be moving like an inverse pendulum - not something to make life easy when mucking about with multiple tons of high explosive and rocket fuel. Reloading hence can only be done on smoother seas, and will take more time.

The U.S. Navy presently has no serious opponents for blue-water supremacy - and most of its actual threats are aerial, submarine or small-boat rather than major surface combatants. As such, it has a need for fast-response and quick salvos of missile weapons for air defense, or heavy missile weapons for long-range shots. There is less of a requirement for sustained missile fire engagements under attack, with ammunition below deck in protected magazines. Rotating launchers with missile handing rails introduce both complexity and delay - which VLS avoids.

Given that the U.S. Navy presently should be able to maintain sea control to the point of being able to find a quiet spot to reload, the disadvantages of the VLS system apparently were not enough to overcome its advantages.

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