Examples of this new trend towards using cold-launched VLS are:
- The Europeans build their equivalent of the hot-launched Mk 41 VLS from the United States in the SYstème de Lancement VERtical (Sylver) VLS. The United Kingdom adopted the Sylver VLS with Aster missiles in their Type 45 destroyers. However, in their future Type 26 frigate, they will also use the smaller and lighter cold-launched Common Anti-Air Modular Missile (CAMM(M)) or Sea Ceptor, based on the ASRAAM missile.
- The Chinese first VLS developed was a cylindrical, cold-launched system in their Type 052C destroyer. This was followed by a hot-launched Mk 41 like system in the Type 054A frigate. Now it appears the Type 052D destroyer will use a new universal VLS combining hot-launch with cold-launch.
Both the European and Chinese hot-launched systems were basically modeled after the 2 x 4 square Mk 41/Mk 48 in general layout and design, featuring a centralized exhaust system.
The Russians have mostly stuck with cold-launch for their VLS, while the US has preferred hot-launched VLS, including in the new Mk 57.
In hot-launched VLS, the missile is fired from within the VLS cell and the missile rocket motor itself propels it out into the air. In cold-launched VLS, there is an additional stage, where the missile is ejected, usually by compressed gas or a piston, out of the VLS cell before the missile rocket motor is fired.
Both system have their advantages and disadvantages and can be more suitable depending on the situation, such as:
- Hot-launched VLS allows faster engagement of the target, while cold-launch is delayed by the extra ejection stage. However, in general, the shorter the target distance, the less suitable either VLS becomes, such as in Close-In Weapon Systems (CIWS) where every second is crucial. In this case, a more horizontal and direct launch path is preferable such as adopted by the Rolling Airframe Missile (RAM) or HHQ-10 / FL-3000N.
- Hot-launched VLS necessitates a complex, large and heavy venting and exhaust system, while cold-launched VLS does not. This allows much bigger and heavier missiles to be integrated with cold-launched VLS. Beyond a certain limit, hot-launched VLS exhaust cannot safely deal with excessive heat and fire generated by larger missiles and may cause damage to the ship.
Possible problems with cold-launch such as the missile falling back after failure of the rocket motor to ignite has reportedly in Russian and Chinese service been insignificant and not more likely than other possible missile malfunctions in hot-launched systems.
The Chinese have adopted the military standard GJB 5860-2006, which seeks to create a hybrid VLS, which combines the advantages of both hot-launch and cold-launch by supporting both.
The Chinese have until now used both VLS systems, sometimes at the same time. For example, the HQ-16 / HHQ-16 comes in both a cold-launched version and a hot-launched version.
The new VLS has no central and shared exhaust system, but only when necessary, will each missile cannister have their own exhaust system. This takes up space alongside the square edges and reduces the thickness hot-launched missiles can have. When not necessary with cold-lauched missiles, almost the entire cell diameter can be used.
The Chinese modular VLS, which looks to make its debut on the Type 052D destroyer can:
- Support both current and future hot-launched missiles like the HHQ-16 and cold-launched missiles such as the HHQ-9. Quad-packed missile canisters in one VLS cell similar to ESSM can also be integrated such as the DK-10.
- Various versions come in different canister length, such as 9000 mm, 7000 mm and 3300 mm for ships of different displacement. Each canister has a diameter of up to 850 mm.
The VLS can be used against all targets:
- In the air with surface-to-air missiles
- At sea with anti-ship missiles
- On land with land attack cruise missiles
- Under water with anti-submarine rocket assisted torpedoes
The addition of cold-launch and larger cells allows the integration of much larger missiles than has been seen in the past without taking up too much space in the confines of each ship.
If the hybrid system works in practice, it could offer crucial advantages in for instance anti-ballistic missiles or anti-satellite applications, where larger missiles could greatly increase the scope of high-altitude exoatmospheric engagement.