I’ve written in the past about the use of land-based air defense systems for pressuring adversary air forces’ wartime ability to fly through a maritime chokepoint. Though these systems would not be able to ‘shut the door’ completely against a capable adversary, they could still help reduce the number of adversary aircraft on the margins that could break through the chokepoint in any given raid. This would be of considerable value to a U.S. campaign to protect the sea lines of communication to its East Asian allies in the event of a war with China, or in some scenarios to protect NATO sea lines of communication within the Eastern Mediterranean in a war with Russia. As John Stillion and Bryan Clark point out in their new CSBA study investigating historical competitions between opposing battle networks, actions that disrupt an adversary’s plans or prevent him from achieving his objectives often generate far greater strategic gains than is possible via a singular focus on attriting the adversary’s forces. The latter is often very important to achieving the former; it just isn’t necessarily the only or the most achievable means to that end.
It is clear, then, that
land-based air defenses can be of considerable indirect value to the screening of
friendly shipping. But could they also contribute more directly in that
mission? Could they be used to substitute in part for escort combatants? The
story’s much more mixed on that front.
The first limiting
factor is air search radar coverage. A traditional radar can generally only search within
its line of sight. The Earth’s curvature affects this the most; for example, a
radar mounted 100 feet above sea level will generally be blind to an aircraft
200 miles away that descends below roughly 17,400 feet. Land terrain along the radar’s
line of sight only reduces the searchable volume further; this will constrain
where a land-based radar can be placed if seaward coverage is desired. And all
this assumes the aircraft’s radar cross section is large enough to allow for
detection.
These factors can be
overcome somewhat by using a distributed fire control network. In theory, an AEW
aircraft that detected an adversary’s aircraft (or cruise missile) could
transmit fire control-quality radar data to a friendly land-based air defense
system. Should the AEW aircraft and the land-based system use highly
directional line-of-sight communications to exchange this data, the adversary
would find it extremely difficult to intercept let alone exploit the networking
pathway.
Even so, this feeds
into the second and far more impactful limiting factor: the interceptor missile
range and engagement geometry. Pick any U.S. longer-range surface-to-air
missile: its maximum advertised range is generally not too much more than 200 miles
or so. But this does not reflect the missile’s actual effective range against a
particular target aircraft (or cruise missile) in a given scenario. An
engagement geometry involving an interceptor flyout that’s more-or-less
tangential to the target’s trajectory would have a much shorter maximum
effective range than one in which the intercept is nearly head-on. A geometry
in which the interceptor would have to overtake the target would have an even
shorter maximum effective range. Even if kinematically possible, engageability
opportunity windows might be very short based on the interceptor’s flyout
distance at a given geometry. The bottom line is that a land-based
surface-to-air missile would not be able to directly screen naval forces or
protected shipping in waters outside the missile’s engagement envelopes.
In theory, then, a
land-based air defense system might at best be able to help screen shipping in
the terminal approaches to a friendly coast. An adversary probably would not
hazard its maritime strike aircraft in these waters if segments of the
defender’s sea lines of communication lay outside that coverage. In contrast,
the adversary might be very willing to use missile-armed submarines inside
these waters. A high-speed anti-ship cruise missile fired by a submarine at a
target 60 miles or less away (consistent with an attack from the second
convergence zone, if one is available) would be very difficult to intercept
unless an air defense system was positioned fairly close to the threat
missile’s trajectory. It’s hard to see how a land-based air defense system,
even if supported by distributed fire control from an AEW aircraft, could make
that kind of intercept.
We can therefore see
that direct protection of shipping at sea would depend predominantly upon the screening
forces interposed between an adversary’s raiders and their targets. Ideally
there would be an outer layer consisting of aircraft and an inner layer
consisting of escort combatants. If the waters being traversed by a convoy or
other protected shipping were outside the effective range of land-based
aircraft, carrier-based aircraft might be usable in their place. If carrier
support was unavailable, then area air and anti-ship missile defense would
entirely depend upon the availability of Aegis combatants. If there were
insufficient Aegis combatants to provide this coverage, then the escorts and
their charges would be on their own.
The views expressed herein are solely those of the author
and are presented in his personal capacity. They do not reflect the official
positions of Systems Planning and Analysis, and to the author’s knowledge do
not reflect the policies or positions of the U.S. Department of Defense, any
U.S. armed service, or any other U.S. Government agency.
