When people describe ships that they’d like to see designed, one of the most common characteristics is more VLS cells. Seems reasonable, doesn’t it? More cells means more offensive or defensive power, right?
Well, there’s a few things wrong with that concept.
For starters, there’s the matter of inventory. Our current fleet has around 9000 VLS cells. What’s our inventory of Standards and Tomahawks that could, potentially, fill those cells? No one knows, or, at least, I don’t. However, going back over purchase announcements for the last several years suggests that our inventory of Tomahawks is around 3000 or so. If the Standard inventory is similar, that would suggest around 6000 missiles to fill 9000 cells. Hmm … We would seem to be a bit short on missiles compared to cells. If true, that suggests that the desire to put more cells in ships may not be a worthwhile design goal. Now, I readily admit that I don’t have definitive numbers for the missile inventory but I have done my homework on what’s available in the public domain. I don’t think I’m too far off one way or the other. I’m making some allowance for usage, both combat (we seem to periodically shoot off a hundred or so missiles in various conflicts) and training, as well as shelf life limits and electronic diagnostic failures.
Of course, there’s no requirement to be able to fill every VLS cell at the same time. Even in a war a certain percentage of ships would not be deployed at any given moment. That said, the difference between an inventory of 6000 and a capacity of 9000 is well beyond the vagaries of deployment schedules.
|VLS - More or Less?|
The example of Harpoon missiles is instructive. While we technically have an inventory of thousands of Harpoons, relatively few of them are serviceable. They’ve all exceeded their official shelf lives and are being rotated into storage as they fail their diagnostic checks. We have very few usable Harpoons left. I don’t know the situation as it applies to Tomahawks but I suspect that shelf life is a serious issue.
Another problem with larger numbers of VLS cells is the impact of combat loss of a ship. Historically, most (all?) ships that are sunk do so with the majority of their magazines unexpended. Thus, the more loaded cells there are on a ship, the more unexpended missiles we’ll lose when a ship is sunk. This goes directly back to the inventory issue. To take an extreme example for illustrative purposes, if a ship with 1000 loaded VLS cells is sunk, we’d probably lose 95% of the missiles still unfired. That’s quite an inventory loss for little gain. On a related note, this is one of the problems with the old Arsenal Ship concept. It’s a lot of eggs in one basket.
The only time we’d really need large numbers of VLS cells on a single ship is for high volume Tomahawk land attacks or, to an extent, saturation or long duration AAW scenarios. Even the saturation AAW scenario probably doesn’t justify too large a number of cells. Remember, only a relatively few missiles can be in the air at any given time. Thus, having a hundred or two hundred cells worth of Standards won’t get more than a small portion of them into the fight before the attack is over – incoming high subsonic or supersonic missiles don’t allow for a very long engagement window. Land attack would benefit from larger numbers of VLS cells (the Arsenal Ship concept), however, it also suffers from the “all your eggs in one basket” risk.
Most people seem to think that the more VLS cells a ship has, the better its ability to conduct AAW and defeat incoming missile attacks. The reality is that a single ship with a million VLS cells is no better than a single ship with six VLS cells in a single missile engagement. This is due to the illuminator limitation issue (you can only guide a few missiles at a time even with terminal-only guidance) combined with the very short engagement window for a modern anti-ship missile.
The only benefit that additional VLS cells offers in an AAW engagement is that the ship can conduct AAW for a longer period of time. Again, though, remember that even a saturation attack won’t last very long.
These issues suggest that there is an optimum balance of number of cells versus risk. I don’t have the actual performance data to be able to state what the optimum number of cells should be but I suspect that around 100 cells is about right – basically a Burke. Much more than that and you run the risk of losing too much inventory for too little gain.
The exception, or modification, to the risk issue is the SSGN. Due to the inherent stealth of the SSGN it can carry more cells for the same relative amount of risk. Indeed, the 150 or so cells the SSGN carries represents a potent offensive strike while minimizing the risk.
Now, if the Navy ever develops a new anti-ship missile that is VLS capable that will change the equation. Additional cells will be needed to field a credible surface strike. That may change the ideal number of cells but it won’t change the concept that there is an optimum balance point.
All that’s fine but what if we want to accept the risk? What’s the problem with having more cells? Well, the answer is cost. VLS isn’t free. Aside from the obvious cost of the VLS module itself, each module consumes precious ship’s internal volume and deck space, which translates to larger ships and bigger engines to move the ship. That in turn requires more fuel, the storage of which requires a larger ship. In addition, the VLS modules use the ship’s utilities (power, water, etc.).
We see, then, that VLS cells should be added only if absolutely required to meet the ship’s mission.