electrical power, and communications to the vehicle from a rather large sur- 

 face support craft. The submersible is rather uncomplicated in nature, but 

 its maneuverability is poor. The tethered vehicle incorporates an umbilical 

 cable which provides electrical power and communications (figure IB). Because 

 the cable no longer supplies mechanical power to the vehicle, the cable is 

 lighter and more flexible and the support ship's size requirements are re- 

 duced. Maneuverability of the vehicle is such that undersea inspections and 

 work operations are possible. The recent appearance of the free-swimming un- 

 manned submersible has been made possible because of advances in LSI technol- 

 ogy and the development of microcomputers. In this case, the approach to the 

 extension of man in the underwater environment actually crosses the line be- 

 tween projection and replacement. Figure 1C shows a supervisory-controlled, 

 free-swimming vehicle. Because this configuration requires only a communica- 

 tion link to the surface support ship, the vehicle has many of the tethered 

 vehicle's advantages of maneuverability for inspection and limited work mis- 

 sions without the problems associated with a tether. Eliminating the tether 

 offers the vehicle the performance advantages of (1) higher speeds due to the 

 reduction of cable drag and (2) entanglement-free operations around struc- 

 tures. Note that because the tether is eliminated, there is no need for ship- 

 board storage of the cable during transit, for a cable-handling system and its 

 associated manpower requirements, or for station keeping during an operation 

 at sea. Thus, the support ship requirements are again diminished with respect 

 to size and, consequently, operating costs. If the communication requirements 

 for the free swimmer are reduced to zero, a totally autonomous submersible can 

 be produced (figure ID). The support ship is then eliminated, and the 

 approach to underwater operations becomes that of replacement. All the 

 brainpower, sensors, effectors, propulsion, and power source requirements for 

 performing a given operation are contained within the vehicle itself. It is 

 thus possible for a single vehicle to incorporate both projection and 

 replacement modes of operation depending upon the task undertaken. 



Based on the above discussion, the terms free-swimming or untethered, 

 unmanned submersible do not necessarily refer to autonomous vehicles. Con- 

 versely, one cannot imply that a free-swimming unmanned submersible is im- 

 practical, if there is no direct method of communicating with it during a 

 given operation. Certain totally autonomous operations are practical even 

 with today's technology. This has become increasingly evident as the devel- 

 opment of the testbed free- swimming submersible described in this report has 

 progressed. 



For the past several years, the Naval Ocean Systems Center (NOSC) has 

 been involved with the development of small, unmanned vehicle systems. The 

 list of these submersibles includes the first hydraulic Snoopy, the Submerged 

 Cable-Actuated Teleoperator (SCAT), Electric Snoopy, NAVFAC Snoopy, and the 

 Mine Neutralization Vehicle (MNV). The development of control for these 

 vehicles has progressed from being completely manual using hardwire cable to 

 having some automatic control circuits directed by a lightweight, low-drag 

 cable with multiplexed data and control signals. The general trend of teth- 

 ered vehicle design is toward more autonomous control (see table 1). The 

 microprocessor has allowed simplification of the hardware required for small 

 unmanned vehicles, i.e., the designer has replaced much of the hardware con- 

 trol with flexible software allowing the vehicle considerable flexibility in 

 meeting changing mission requirements. 



