This is such a good question, I decided to stop what I was doing to answer it. Why are short range ballistic missiles considered to be such a potent threat when we usually tend to think of longer ranged weapons as more strategically valuable? And the answer all comes down to timeline. I’ll give you the bottom line up front, and then we’ll go back for some more detail.
The long and short of it is that intercepting a ballistic missile is a very complicated multi step process and the shorter the distance the weapon needs to cover, the less time you have for each of those steps. But to get a bit more granular here, ballistic missiles derive their name from the high arcing ballistic flank path that they follow on their way to their target, regardless of the range of the weapon. For the sake of an intercept, we split that hierarchy ballistic flank path into three separate phases. First, you have the boost phase, which very literally looks like and is a rocket launch. This is the face of life when the missile is flying under power, rapidly collecting both speed and altitude. Then you have the mid course phase. This is where you’ll find the apogee of that ballistic flank path. In other words, this is the peak of that high arc. This often begins when the warhead separates from the booster and is coasting unpowered at the peak of that arc, usually in space. And then we have the terminal phase as the warhead reenters the atmosphere and closes with its target at extremely high speeds, often above Mach 20.
Now, it is theoretically possible to conduct an intercept in any one of these three phases. But that depends very much on your awareness of the launch, the capability of your systems and your proximity to the launch itself, intercepting a ballistic missile during its boost phase would invariably require being close enough to the launch to fire an interceptor at that missile and hit it before it gains so much speed that you can’t catch up.
As a result, the United States and really just about everybody tend to prioritize intercepts in the mid course and terminal phases. In the case of the United States, a mid course intercept might be conducted by Aegis Combat System equipped US Navy destroyers or cruisers launching SM3 interceptors. We saw that not long ago in the Red Sea or maybe most notably America’s Homeland Defense ground based Mid course defense system. Terminal phase intercepts on the other hand might be handled by those same age is equipped worships leveraging an SM6 interceptor, maybe a Patriot air defense system, launching a Pack 3 interceptor or the incredibly capable fad system, which is short for Terminal High Altitude Area Defense.
And remember when I said that conducting an intercept is a complicated multi step process? Well, depending on who you ask, that process may have as many as eight separate steps, each of which take time. Now, intercontinental ballistic missiles are exceedingly fast. In fact, they can regularly reach their target faster than a modern hypersonic missile could because hypersonic weapons are maneuvering along the way. America’s Minute Man 3 ICBM, for instance, will regularly break mock 23 during its terminal phase. But nonetheless, depending on the launch location, intended target and the specific type of weapon itself, it may take anywhere from 20 to even 40 minutes for an intercontinental ballistic missile to go from launch to impact. And since it can often take a solid five minutes to detect the launch and relay that information to defensive systems, that means you’ve usually got at least 15 minutes to go through all eight of those intercept steps. Short range ballistic missiles, on the other hand, are a fair bit slower, usually topping out at between Mach 3 and Mach 8. But because they’re covering such a short distance, your timeline is still significantly shorter, often between just five and maybe 15 minutes. And as I just pointed out, it is not unreasonable to expect that it may take up to five minutes to detect the launch and relay that information to the pertinent defensive systems and command elements, not to mention any potential decisions that may need to be made about whether or not the weapon actually poses a threat and what type of interceptor to use, though, to be clear, in most of today’s advanced air defense systems, those decisions are usually automated. Nonetheless, this means that while there are no absolutes in combat, it’s entirely possible that you may be hit by a short range ballistic missile before you even know it was launched. So why are short range ballistic missiles such a big deal? Well, they’re awfully tough to defend against and there’s no way to discern between a nuclear armed and a conventionally armed ballistic missile until it makes landfall. And as a result, having these weapons in service arguably increases the risk of global nuclear war.