Armored Sensors

One of the arguments against armor on ships is that the ship’s sensors can’t be armored and allow for an easy mission kill so what’s the point of any armor?  This train of thought is illogical and idiotic but that’s not the point of this post so …
 
It is taken as an article of faith that ship’s sensors can’t be armored.  How could they be?  If they’re armored, the sensors will be blinded, right?  As we do with so many widespread beliefs, let’s examine this and see if it’s really true.
 
Where do we always start when examining anything?  That’s right: history, of course!  What can history tell us about sensors and armor?
 
 
Land combat
 
Historically, sensors, meaning eyeballs and optical aids, were protected by placement behind trees, rocks, walls, bunkers, etc.  This was highly effective armor (armor being any object or material that protects the sensor).  The sensor needed only a tiny opening in the armor to observe the relevant field of view.  A mere slit or hole was sufficient to allow the sensor to function.  If the observer wanted hemispherical sensing then he merely turned around and “re-aimed” the sensor, poking a new hole in the armor, if necessary.  We see, then, that sensors have always been ‘armored’ and their field of view unimpeded by the armor.
 
 
Tank sensors
 
Tanks offer a specific and more applicable example.  Tank sensors, originally eyeballs and optical aids but now including infrared, low light, radar, laser rangefinders, etc., are embedded inside heavy tank armor with, again, small openings aimed at the field of view.  Many tank sensors are able to rotate to allow the sensor to cover large arcs or 360 degree fields of view.  Alternatively, many tank optical sensors (eyeballs) have armored, reflective/mirrored observation blocks arranged in a circle around hatches thus providing 360 degree observation and alleviating the need to stand up in the hatch to observe the surroundings.  In addition, most tank sensors can be sealed with armored covers when not directly in use thus making the sensors highly survivable.  Finally, some sensors are duplicated around the tank so as to provide continuous 360 degree coverage (active protection radar systems, for example).  Thus, tank sensors are both physically armored and ‘armored (made survivable)’ by duplication while allowing unimpeded sensing.
 
As seen in the photo below of an Israeli Merkava tank, the optical sensor is protected in an armored box-like housing with a closeable shutter to completely protect the sensor.  The optical sensor needs only a small vertical slit opening to function.
 
Also visible is a small radar array for an active protection system.  The array face is not armored but the location ensures that the array is protected on the back and sides by the bulk of the armored turret while being able to scan the 120 degree or so field in front of it.  Thus, siting the sensor next to an armored structure (the turret) provides ‘neighborly’ protection regardless of whether the sensor housing itself is armored.  On a ship, this suggests that sensors could be similarly mounted near/next to other armored structures and gain indirect armor protection.
 

Merkava Optical Sensor with Shutter and Slit Opening,
Note Radar Array at Far Left

 
 
Ship sensors
 
WWII large caliber naval guns included armored, optical rangefinders as part of the structure of the turrets.  These were typically housed in the ‘ears’ that stuck out from the rear sides of the turrets.
 

Note the armored ‘ears’ sticking out the sides
 of the turret near the back which housed
the local, optical rangefinder components

 
Larger guns also used armored directors.  The Iowa class battleships, for example, used a pair of Mk38 directors.
 

As built, all three turrets on the Iowa class had 25 power, 46 foot (14 m) rangefinders, with Stereoscopic Mark 52 used in Turrets II and III and Coincidence Mark 53 in Turret I. The Mark 52 weighs 10,500 lbs. (4,763 kg) and cost about $100,000 US during World War II. Near focus for the Mark 52 is 5,000 yards (4,570 m) and the maximum range is 45,000 yards (41,150 m). Mark 53 was a coincidence type with a special astigmatic lens which allowed it to range in on a single point source, such as a searchlight.[1]

While lacking a reference for an exact armor description and thickness for the Mk38 battleship fire control director, US Naval Weapons notes:
 

The principle of protection for fire control may be noted;  the main battery fire controls, and particularly the main battery rangefinders, were all under armor, consistent with the armored protection of the main battery itself.[3]

This suggests that the rangefinder shared the turret’s armor of 9-19 inches.
 

Mk38 Director

Even the secondary directors were armored.  The Iowa class 5” secondary mounts were controlled by 4x Mk37 secondary fire control directors.
 

The Director was enclosed in a Shield made of 3/4 inch thick armor plate that rested on a Carriage at the bottom of the Director. The Carriage turned on roller bearings in the Roller Path on the Base Ring. The Base Ring was attached at the top of a 9 foot 4 1/2 inch diameter, 14 foot 3 inch high cylindrical Barbette of 3/4" thick specially treated steel armor plate. The mating surface of the Barbette was machined in place, after installation on the ship, to be parallel to the Turret and Mount roller paths to minimize alignment differences between the rotation axes that could affect aiming accuracy. A 22 inch diameter internal cable tube hung from the bottom of the Carriage to carry cables to the ship below. Beneath this was another 22 inch dimeter cable tube fixed to the O5 Level deck. Below this was a 31 1/2 inch diameter Director Tube of 3/4 inch thick steel that descended to the Third Deck to carry the cables down to Gun Plot.[2]

Mk37 Director

 
We see from this description that rotating, armored sensors were a common item on ships.
 
When radars were added to the directors, the radars were, of course, not armored.  Their locations, high atop the superstructures did provide a measure of protection from shrapnel but the exposed radars were susceptible to damage.  This vulnerability was mitigated by duplication;  multiple directors greatly increased the odds on director survivability.
 
On a more modern note, the Swedish Visby class corvette incorporates a retractable navigation radar.  Visby’s superstructure is not armored but there is no reason why it could not be and then the radar would be protected within the ship’s structure until needed.
 
Another example of hidden, protected sensors is the San Antonio (LPD-17) class which has its sensors enclosed in a composite mast.  The mast enclosure is not armored but does prove that sensors can be enclosed given a suitably emission-transparent surrounding material.
 
 
Ship Weapons
 
While not sensors, modern weapons have been armored or hidden from exposure without compromising their performance.  For example, the defunct Advanced Gun System (AGS) on the Zumwalt had its gun barrel hidden inside a stealth housing from which it would elevate when in use.  Similarly, several warship designs have placed missile rack launchers behind and below elevated ship sides (in a “pit”, essentially) which could easily be armored.
 

Ambassador MkIII - note missile launch 
racks in 'pit' amidships

Discussion
 
It is clear from history that sensors have commonly been protected and armored by various means without impeding the sensor’s function.  That’s just common sense.  Firepower without sensors is nearly useless so it makes sense to protect and armor the sensors, if at all possible.  It is only in recent decades that we’ve stupidly abandoned armor and protection for our weapon sensors.
 
It is clear that there is no reason why sensors can’t be housed inside armored enclosures, one way or another.  Let’s consider our current sensors. 
 
The common US Navy sensor is the flat panel radar array.  There is no reason why panels can’t be equipped with armored shutters that can slide into place when the sensor is not in use. 
 
The America class LHA uses SPS-48/49 radars but they serve no real purpose since the LHAs will always be accompanied by Burke class escorts with their Aegis SPY panel radars.  A smaller TRS-3D/4D would be perfectly appropriate for the LHAs and could easily be mounted inside rotating and/or retractable armored enclosures.
 
Ship mounted Infrared and optical (IR/EO) sensors are small and readily lend themselves to tank-like armored enclosures with small, shuttered openings for their field of view.  The sensors can be either fixed and mounted at multiple points around the ship to provide hemispherical coverage or mounted inside rotating armored cylinders for complete coverage.  Retractable mounts would be equally effective.
 
So, with a combination of armored covers, retractable sensors, rotating armored enclosures, and tank-like enclosures we could easily armor our sensors, preventing cheap mission kills from simple shrapnel.  This would be a major step towards keeping our ships fighting while taking hits – a presumed goal of every WARship design.
 
 
 
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[1]http://navweaps.com/Weapons/WNUS_16-50_mk7.php
 
[2] https://www.okieboat.com/Gun%20Director.html
 
[3]Norman Friedman, US Naval Weapons, Naval Institute Press, 1985, ISBN 0-87021-735-6, p.36