ASW Drones

Unmanned is the fad of the day and using drones for anti-submarine warfare (ASW) is an idea that keeps cropping up.  So many people seem enamored with the idea and yet no one has examined the actual use.  Typically, proponents enthusiastically cite the usual drone characteristics, such as extended endurance, without understanding what that means … or doesn’t.  Let’s take a closer look and see if ASW drones are a good idea or not.
 
Let’s examine the characteristics, claimed and actual, of an ASW drone.
 
Endurance.  Proponents claim that the greater endurance of drones will revolutionize ASW, however, that ignores the reality that once any ASW aircraft, drones included, have expended their weapons/sensors they become useless regardless of their remaining endurance.  A drone with a month’s worth of flight time is finished as soon as its sonobuoys and/or weapons are expended.  It doesn’t matter how much longer it can fly.  ASW aircraft are sensor/weapon limited, not endurance limited.  Thus, drones offer no advantage and, in fact, depending on the exact drone, would very likely have fewer sensors/weapons than a manned aircraft and would, thus, have LESS effective endurance than a manned aircraft!
 
Signal Processing.  Manned ASW aircraft such as the S-3 Viking, P-3/8, and helos carry on-board computers and analysts to interpret the sensor signals.  Drones have no on-board analysis capability and must continuously communicate with the host ship.  This is a continuous, broad band transmission which is highly susceptible to detection and localization by the enemy.  The host ship, in turn, has to broadcast control signals to the drone.  Elementary analysis of the locations of drones performing ASW reveals the likely location of the host ship to the enemy.
 
Size and Operation.  Proponents never quite specify the size of the drone they’re calling for.  There are only two possible drone platforms, currently:  Burkes and amphibious ships.
 
The reality is that destroyer size ships (like a DDH) have no large flight deck or recovery area and are limited to something in the Scan Eagle size (5 ft long, 10 ft wing span, 30-40 lb empty weight, 11 lb payload) or the somewhat larger helo-type UAV such as Fire Scout.
 
Helicopter carriers could operate larger drones but even they have limits.  For example, the Wasp class LHD has a [roughly] 104 ft wide flight deck.  A commonly cited drone is the MQ-9 Reaper and I'm moderately sure that, in theory, a 1000 ft x 104 ft flight deck would allow a Reaper to take off. The caveat is that the Reaper does not have an immensely powerful engine so the acceleration might, actually, turn out to be insufficient. That would have to be tested but, for the sake of further discussion, let's assume it could take off.
 
More problematic is that the Wasp island extends close to half way across the flight deck amidships. That reduces the usable flight deck width to around 50 ft, at that point. The Reaper has a wingspan of 65 ft. which puts the nose wheel at 33 ft from either wing tip. Allowing for, say, 10 ft of wing tip clearance from the island (the Navy would probably insist on a greater safety margin than that), that would put the nose wheel 43 ft away from the island which would be within 10 ft or so of the deck edge. That, in turn, puts the wing wheels within a few feet of the deck edge. The slightest deviation and the aircraft is off the edge! In short, it would seem that the full length of the deck cannot be safely used. That leaves only a few hundred feet forward of the island for takeoffs. Now, I'm really not sure an unassisted takeoff is possible!  In fact, it seems unlikely.
 

Wasp Class - note the island extending into the flight deck

So, a Reaper would be the maximum size drone that could operate off a big deck amphibious ship with catapults and arresting gear and it’s likely even that is too big. 
 
Of course, we could purpose design a drone carrier that could operate large UAVs but that would be decades down the road and, likely, unaffordable if we continue buying $20B Fords.
 
Then, there's the issue of storing/hangaring large UAVs (Reaper is 36 ft long x 65 ft wide, for example). It would need some serious wing folding to get an acceptable spot factor so that we could operate more than one UAV.
 
Carrier Adaptation.  Adaptations such as beefed up landing gear, arresting hooks, folding wing mechanisms, etc. all add weight to the aircraft and negatively impact already limited payload capacities as well as unaided takeoff and landing distances.
 
Payload.  To give some frame of reference as we talk about drone payload capacities, here are some relevant sensor/weapon weights:
 
Sonobuoy - 35-40 lbs, depending on specific type
Torpedo - The Mk54 lightweight torpedo weighs a little over 600 lbs.
 
What is a useful payload size and composition?  A reasonable minimum would be something on the order of 40 sonobuoys and 2 lightweight torpedoes.  Thus, a payload of two torpedoes plus 40 sonobuoys = 2800 lbs without launchers, pylons, and associated equipment.
 
Drone payload capacities vary widely, depending on the size of the aircraft.
 
Drone Types.  With the characteristics we just discussed in mind, let’s now review the basic drone types and see how they mesh with the characteristics.
 
Small.  Small UAVs, such as Scan Eagle or RQ-21 Blackjack size, can operate off destroyers.  The drawback is that they have a very small payload to the point of being incapable of effective ASW work.
 
Scan Eagle, as an example, is very small and has a mere 11 lb payload capacity.  A standard A-size sonobuoy is around 5” diameter x 36” long and weighs 39 lb.  A Scan Eagle size drone couldn’t even carry one sonobuoy! 
 
Medium.  Intermediate size UAVs such as the vertical takeoff and landing MQ-8B Fire Scout has a theoretical maximum payload of around 500 lbs, however, the practical payload is around 100 lbs.  Thus, it could not carry even a single torpedo and only a few sonobuoys.  This is simply not an effective payload. 
 
The larger MQ-8C Fire Scout has a maximum theoretical payload capacity of around 700 lbs with a practical payload of around 300 lbs. 
 
These drones are capable of operating off a destroyer but cannot carry a combat-useful payload.

Fire Scout

Large.  Larger UAVs such as the MQ-9 Reaper, Predator, Global Hawk, etc. have payload capacities that begin to be useful but they require actual aircraft carriers with catapults and arresting gear to operate from.  The MQ-9 Reaper, for example, has a theoretical maximum payload of 3800 lbs and a practical capacity of around 1000 lbs on a wingspan of 65 ft and a length of 36 ft. 

 
 
Land Based
 
So far, we’ve limited our discussion to ship based drones but land based drones are also an option.  While concerns about takeoff/recovery are not an issue, payloads, effective endurance, and signal processing communications are and still impose limitations.
 
Presumably, most naval operations will occur well out to sea (thousands of miles) which is certainly within reach of large UAVs (noting, of course, the inverse relationship between payload and range/endurance!) but is not a tactically responsive situation.  For example, a surface group that requests drone ASW support will have to wait many hours for a response under even the best of circumstances.  Land based ASW aircraft, whether manned or unmanned, are best employed as a base defense rather than as a task force support asset. 
 
Attempting to supply a constant ASW presence using land based aircraft would require a constant stream of aircraft flying to and from the operating area.  It would require something on the order of a dozen aircraft to maintain one continuously – and effectively – on station.  Remember, that in a war, sonobuoy and weapon usage will be staggering and all the endurance of an aircraft will be rendered moot as the aircraft quickly empties its payload and is rendered ineffective.
 
 
Conclusions
 
1. Very small drones can operate off destroyers but are incapable of performing any effective ASW due to payload limitations.
 
2.  Larger, vertical takeoff UAVs can operate from destroyers but, again, their payloads are so limited as to render them nearly useless and not worth the support and operating effort.
 
3. A big deck amphibious ship for moderate size UAVs is feasible although they would likely need to have catapults and arresting gear.  Again, there are payload concerns although they begin to approach a somewhat useful load.  This is an expensive option.
 
4. Land based ASW drones could possibly carry a useful payload but are tactically inefficient and are best relegated to patrolling around their base.
 
5. A reasonable alternative would be to modify a large commercial vessel to operate large UAVs by eliminating/minimizing superstructure and adding a long flight deck.  This would likely be the cheapest and best option.
 
 
Considering the above conclusions, it is hard to visualize effective, efficient ASW drones.  They simply don’t have the characteristics necessary to perform combat-effective ASW.  In other words, there is no viable CONOPS for ASW drones.  Further, given that we have existing ASW helos and P-8 Poseidons, one has to wonder why so many people want to force fit drones into a task they are clearly not suited for.