text: referring to fig1 it will be seen that an illustrative water vehicle 20 having mounted thereon an illustrative direction control means 30 may comprise an underwater vehicle 21 and a plurality of symmetrically disposed arrays 32 extending from an aft portion 24 of the vehicle 20 . the vehicle 20 includes at least a portion 26 thereof which remains submerged during travel of the vehicle 20 through the water . when the vehicle 20 is a torpedo 22 ( fig1 and 2 ) or other underwater vehicle ( fig3 ), the entire vehicle is underwater throughout at least a portion of the travel of the vehicle . however , in the case of surface vessels ( fig4 ), only a portion of the hull is underwater when the vessel is underway . referring to fig5 - 7 , it will be seen that the control means 30 may comprise a single array 32 mounted at the aft portion 24 of the vehicle 20 ( fig5 ), generally amidships ( fig6 ), or near the bow ( fig7 ) of the vehicle 20 . each of the arrays 32 includes a multiplicity of fins 34 in a compact grouping for contact with the water through which the vehicle moves . referring now to fig1 , each fin 34 preferably has a neutral - lift , uncambered , cross section chosen to substantially match the hydrodynamic streamlines about the fin present during movement of vehicle 20 through water at below - cavitation - threshold speed , represented by flow arrows 36 . such shape of streamlines is obtainable employing principles of analysis known by those having skill in the art . one such embodiment , shown in fig1 , has a cross sectional shape of an ellipsoidal leading edge 38 with a taper pinched trailing edge 40 . a fin 46 as shown in fig1 may be provided as one of an array of such fins or may be an independent single fin . referring to fig1 for example , the aftermost fins 46 may be at least in part of the aforementioned shape - memory material , such that the fins 46 may be modified in shape by application of electrical current thereto . the array 32 of many relatively short fins 38 oriented generally in the direction of water flow about the vehicle , presents a large surface area when disposed at a selected angle to the flow . the device produces a high force / movement , even at low speeds . the fins 34 may be surrounded by , and attached to , a shroud 42 , as shown in fig1 - 7 and 9 - 15 , or may , as is shown in the aforementioned related applications , be of a configuration wherein all ends of fins are fixed to the shroud , or wherein the shroud to which the fin ends are fixed does not surround the fins . the control assembly fins 34 may be mounted on a central post , with ends of the fins exposed . the fins 46 may be housed within a shroud , or disposed without a shroud , as shown in fig1 . while the arrays 32 shown in fig1 - 7 and 10 extend outwardly , substantially normal to the axis of the vehicle , it will be seen in fig5 that the array 32 of fins 34 may be extended in a position angled forwardly against the direction of water flow . the array may be curved , as shown in fig8 - 10 . as is shown in the related applications , the arrays 32 may be rotatably mounted on the vehicle and / or may be hingedly mounted , so as to be tiltable forwardly and / or rearwardly . as illustrated in fig9 and 10 , vehicle 20 preferably is provided with one or more pockets 50 in the underwater portion 26 thereof . the arrays 32 are movable between positions in pockets 50 wherein arrays 32 substantially conform to an exterior surface 52 of vehicle 20 ( fig8 ) and a deployed position wherein array 32 extends outwardly from exterior surface 52 of vehicle 20 . as seen in fig1 and 13 , the array 32 of fins 34 may include a plurality of first fins 34a parallel to each other , and a plurality of second fins 34b parallel to each other and normal to first fins 34a . the first and second fins 34a , 34b intersect to form a grid - like configuration , with ends 44 of fins 34a and 34b fixed to an inside surface 54 of shroud 42 . in the embodiment illustrated in fig8 - 10 , arrays 32 may be extended by hydrodynamic forces acting thereon as vehicle 20 is launched , or may be extended by spring pressure which operates to fling arrays 32 to the deployed position upon exit of the vehicle from a launch tube . alternatively , the arrays 32 may be selectively extended by power means operative upon signal from a transmitting station , or operable automatically upon lapse of a selected time , or the like . in operation , during tube launch , or when vehicle 20 is moving at high speed , or when the arrays 36 are otherwise not needed , arrays 32 are folded conformal to the body of the vehicle 20 ( fig8 ) upon deployment , the arrays present fins 34 substantially parallel to the direction of flow , minimizing drag . see fig1 , and particularly the arrays 32 shown in phantom . yaw , pitch , and turning control forces may be imparted by angling the array with respect to flow , that is , by angling the array forwardly or rearwardly , or by rotating the array . alternatively , or in addition to such mechanical angling of arrays 32 , a portion of each array may be of a shape memory material such as an alloy of nickel and titanium , known as &# 34 ; nitinol &# 34 ;. nitinol is formable in such manner as to return to a &# 34 ; remembered &# 34 ; shape when heat is applied , as by an electric current . alternatively , components of common piezoelectric materials and electrically inert substrates deform under the influence of an electric current . a device made from such materials can be made to twist , bend , extend , or contract under a controlled electrical input , or other heat source . in a preferred embodiment , shown in fig1 , a strand 60 of shape memory material is attached at its ends to different points on the array 32 . alternatively , the strand 60 may be embedded in a portion of the array 32 , such as in the shroud 42 . upon application of electric current to strand 60 , the strand compacts , or shortens , to alter the shape of the array ( fig1 ). in the embodiment shown in fig1 at the aft end of the vehicle 20 , the entire fin 46 may be of shape - memory material or only a portion thereof . in an alternative preferred embodiment , shown in fig1 , the strand 60 is attached at one end to array 32 and at the other end to surface 52 of the vehicle 20 . upon application of electric current to strand 60 , the strand compacts in length to pull the array 32 from the position shown in fig1 and in phantom in fig1 , to the position shown in solid lines in fig1 . in fig1 , there is illustrated amidship of a torpedo 22 arrays 32 movable between two shapes , a first forwardly leaning shape , shown in phantom in fig1 , and a second shape wherein the arrays are generally normal to the axis of the torpedo . in the forward leaning configuration , water flow through the arrays is substantially parallel to the axis of the torpedo . in the second configuration , the array fins are at an angle to the water flow and serve to slow movement of the torpedo . as will be apparent , by having one array forwardly and the other rearwardly , a turning of the torpedo is effected . strands 60 of shape memory material ( not shown in fig1 ) may be utilized , as shown in fig1 - 14 , to vary the shape of the arrays 32 . in underwater application , the vehicle mounts a symmetric arrangement of two or more shape - adaptive grid fin arrays ( fig1 - 3 and 15 ), or a single large array ( fig5 - 10 ), at tail ( fig1 and 5 ), midbody ( fig2 , 8 - 10 and 16 ), or bow positions ( fig3 and 7 ). the fin arrays 32 are sized as appropriate to the drag , lift , and control needs of the specific vehicle . the array may be enclosed by a streamlined shroud , or open , with blade tips unsupported . during tube launch , or at high speed , or when not needed , arrays 32 can be folded conformal to the vehicle body or otherwise retracted ( fig8 ). they can extend into the flow passively , as by hydrodynamic forces , or under the active force provided by a spring or motor . deployed , the grid fin array 32 possesses a nominal angle of incidence to the flow , at which the fins 34 are parallel to the direction of the flow ( fig1 ) minimizing drag . the array can be built so that this nominal array angle is nonzero ; in fact , the array itself may have a forward , backward , or sideways tilt , or have a curved profile . drag , yaw and pitch control forces are imparted by imparting control currents to the shape - adaptive materials , appropriately angling the array fins 34 with respect to the flow by deforming the entire structure , or by using the shape - adaptive material to alter the blade cross - sections of the fins 34 and / or the fins 46 . the arrays can impart pitch - direction controlling forces in a manner analogous to conventional planar fins by twisting about their axes . importantly , the shape - adaptive grid fin array can impart yaw controlling forces by bending fore and aft ( fig1 ). this additional function distinguishes grid fin arrays from planar fins ; a vehicle can be controlled by a pair of grid fins only , provided they are capable of both fore / aft bending and axial twisting motion . the vehicle can also be braked along its line of motion by bending the grid fin arrays forward or backward in the same direction ( fig1 ) so that off - axis control force components cancel . this function can be performed with arrangements of as few as two grid fin arrays , without imparting rolling forces . the array may be angled forwardly or backwardly to catch or grab underwater cables , poles , or the like , in special applications , and fitted with cutting devices , telemetry interfaces , or latches at its base , discussed further herein . the nominal cross sections of the fins 34 ( fig1 ) making up the grid fin array , and the independent fins 46 , may take any streamlined shape consistent with incompressible hydrodynamic flow , and may be optimized for lift , drag , and / or captivation properties at the foreseen speed ranges of the vehicle . the choice of cross - section may vary from constituent blade to constituent blade , or even within a single blade , to accommodate the complex hydrodynamics of the array geometry . the disposition of the shape - adaptive materials in the grid fin body can take several forms . the materials may be embedded in a flexible matrix during the manufacturing process , or assembled inside or outside the fin in order to impart the appropriate deformation . the shape - adaptive material units may be wire shaped and respond to control input primarily through elongation / contraction . more sophisticated designs may exploit a deformation field arising in the shape - memory / shape adaptive material . additionally , the deformed shapes of the aggregate fin grid or individual fins may result either from the imposition of a control input , or from the absence of such an input . thus , there is provided a control fin assembly featuring a short - chord grid - fin array which permits high forces / moments at low speeds , simple operation , low power consumption , low acoustic signature , compatibility with a tube launch , and retractibility . there is further provided individually mounted and deformable fins . in the aforementioned related patent applications ser . nos . 08 / 411 , 234 , and 08 / 411 , 235 , there are disclosed arrays of fins which are adapted to interconnect with underwater cables . the arrays described herein are adaptable for use as cable interconnect arms , as described in the &# 39 ; 234 , and &# 39 ; 235 , applications . there is thus provided a water vehicle in combination with directional control means which afford high forces / moments at low speeds , simple operation , low power consumption , low acoustic signature and conformability to a launch tube . it is to be understood that the present invention is by no means limited to the particular construction herein disclosed and shown in the drawings , but also comprises any modifications or equivalents with the scope of the claims . for example , while several specific arrangements of fins are illustrated , the fin arrays may be of any shape consistent with incompressible hydrodynamic flow , and may be optimized for lift , drag and / or cavitation properties of a particular vehicle at foreseen speed ranges .