Wednesday, December 11, 2013

Submarine-launched UAVs: Is the Juice Worth the Squeeze?

Last week, the U.S. Navy announced the launch of a fuel-cell powered Unmanned Aerial Vehicle, the XFC, from a submerged nuclear submarine. Interestingly, XFC is at least the fourth sub-launched UAS the Navy has demonstrated.  Previous efforts date back to 2005 and include the hand-launched Dragon Eye and FQM-151 and the sail-launched Buster.  More recently, the Navy first successfully launched a Switchblade from a submerged submarine in Exercise Trident Warrior 2010 using a successor to  Raytheon's Submarine Over the Horizon Organic Capabilities, or SOTHOC launch system.

Other efforts weren't so successful.  The German company Gabler designed the VOLANS (coVert OpticaL Airborne reconnaissance Naval adapted System), a mast-launcher concept which was not constructed. Even more interesting is Lockheed Skunkwork's ridiculously ambitious Cormorant UAV, which apparently never made it past the YouTube stage of development.

More successful however, has been the Tomahawk-land attack missile, which is essentially a one-way fire-and-forget unmanned aircraft that happens to have a 1,000 pound warhead.

But when it comes to conducting intelligence, surveillance, and reconnaissance, many herald the XFC's "new" capability as a game-changer, especially in support of special forces operating ashore.  The basic concept is for a submarine to quietly launch a force of special operators onto a beach and provide that force with over-watch or targeting assistance using the UAV.  Another purpose for sub-launched UAVs would be to extend the submarine's targeting range beyond a periscope and acoustic sensors.  Also, when prosecuting a high value surface target, giving the sub some stand-off to shoot torpedoes or possibly missiles has some tactical merit.  But do these capabilities outweigh the problems inherent  with submarine-launched UAVs?

The primary value of submarines in naval combat is stealth, simply due to the fact that an underwater object is extremely difficult to detect from on or above the ocean's surface.  When a submarine comes to periscope depth, a degree of that virtue is lost.  When a submarine launches weapons, UAVs, or transmits in the RF spectrum, its invisibility is put at further jeopardy.  Besides a possible risk of counter-detection, there are numerous complications with launching a UAV from a submerged submarine.  In addition to the obvious technical challenges of getting a vehicle to transition from a high pressure underwater environment to flight, water-proofing an aircraft's electrical and mechanical systems against saltwater submersion is problematic.

Time lapse shot of XFC sub-launch (USN Photo)
Aside from the Cormorant's implausible recovery scenario using a parachute and an ROV, sub-launched UAVs are designed to be disposable, just like any other weapon.  So they must be used sparingly, and likely only for high end wartime situations.  But over a decade of combat use has demonstrated that the best attribute of UAVs is persistent presence over a target, not one shot, one kill launches. Moreover, in the case of the XFC, torpedo-tube launched UAVs take precious magazine space from additional weapons.  Even so, XFC's fuel cell propulsion solves a sticky problem for the Navy, that of storing combustible UAV fuel onboard a submarine.

A sub must remain at periscope depth to maintain a data link to the UAV or possibly shift control to an air asset or ground station once the vehicle has been launched.  Presumably, if one of these other options were in the area, there wouldn't be a requirement to launch the UAV from a sub.  And there is no reason that special operators can't carry their own small tactical UAVs with them to the beach, eliminating the need for a sub-launched drone.

Despite these drawbacks, certainly the inherent low signature of submarines can be leveraged for unmanned vehicles, especially UUVs, which can be launched, recovered, and controlled by a submarine without having to come to PD.  At some point they Navy may need to come to grips with these issues and write sub-launched UAVs off as a novelty.  Alternatively, it may be possible to develop a UAS that mitigates the above challenges while providing capabilities not found elsewhere in the fleet, but a constrained fiscal environment will make that a challenging endeavor.