2. General Background In military operations, in peace or war time, the maintenance and/or replacement of material and personnel requires a base of operations. Due to political situations, as well as limitations on availability of land, it has become increasingly difficult to maintain a military presence in areas of the world far from the home country. Also, maintaining a military base in several different countries is prohibitively expensive when such bases may not all be needed on a full time basis. This leaves a need for some type of alternative base.

SUMMARY OF THE INVENTION The invention addresses the above need. What is provided is a mobile offshore base. The mobile offshore base is formed from several individual single base units that are connected together at sea to form the complete base. The complete base forms a runway and support base for fixed wing and rotary wing aircraft and also provides space for stowage and transport of equipment and personnel. The single base units are similar semi- submersible units that are linked together by hinges and/or U- joints to form the complete mobile offshore base. Each single base unit is self-propelled and is also capable of independent operations at widely separated locations. The single base units

are each formed from lower hulls, columns that extend upward from the lower hulls, and an upper hull attached to the columns.

BRIEF DESCRIPTION OF THE DRAWINGS For a further understanding of the nature and objects of the present invention reference should be made to the following description, taken in conjunction with the accompanying drawings in which like parts are given like reference numerals, and wherein: Fig. 1 is a perspective view of a single base unit of the invention.

Fig. 2 is a typical transverse section of a single base unit of the inventon.

Fig. 3 is a partial cutaway view of a single base unit of the invention.

Fig. 4 is a perspective view illustrating the single base units of the invention linked together to form a mobile base.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, it is seen in Fig. 4 that the invention is generally indicated by the numeral 10. Mobile offshore base 10 is formed from a number of single base units 12 that are connected together at sea. Each single base unit 12 is generally comprised of at least two buoyant lower hulls 14, columns 16, and upper hull 18.

As seen in Fig. 1 and 2, lower hulls 14 are preferably ship shaped (streamlined with symetrically faired bow and stern shapes) to allow for movement at transit and operating speeds at the efficient power and propulsion capabilities. Propulsion and

dynamic positioning thrusters are indicated by numeral 20.

A plurality of columns 16 rigidly attached to and spaced along the length of the lower hulls 14 extend upwardly therefrom.

Columns 16 are illustrated as being square or rectangular in section but may be of any suitable shape.

Upper hull 18 is rigidly attached to the upper end of columns 16 adjacent outer opposing sides of upper hull 18 such that lower hulls are spaced across the width of the upper hull and are parallel to the longitudinal axis of the upper hull.

Bracing 22 rigidly attached between columns 16 and upper hull 18 provides support to minimize flexing and maintain spacing between the lower hulls 14. Upper hull 18 is sized and constructed to form an upper deck 24 and, in the configuration illustrated, three lower decks 26. Upper deck 24 serves as an aircraft runway and landing area for fixed and rotary wing aircraft as well an apron for loading and unloading the aircraft. Lower decks 26 are used for living space and storage space for equipment and supplies. Fig. 3 illustrates loading and storage capabilities.

Each single base unit 12 is provided with variable ballast tanks 28 in lower hulls 14 and columns 16. Variable ballast tanks 28 provide for operation as a semi-submersible vessel to selectively allow operation at different drafts. At transit draft, the hulls 14 are at their shallowest draft and allow for top speed. At operational draft, illustrated in Fig. 4, lower hulls 14 are fully submerged below the water surface to provide, relative to transit draft, a smaller water plane area through hull that greatly reduces pitch, roll, and heave in response to

wave action. Survival draft is selected during storms. Variable ballast tanks 28 are operated to receive or expell water ballast in a manner well known in the art.

In operation, each single base unit 12 may be used individually or one or more may be connected together as illustrated in Fig. 4 to form a mobile offshore base suitable for receiving fixed and rotary wing aircraft. In this configuration, the connected units are preferably ballasted to an operational draft as illustrated to minimize motions from waves. For the purposes of forming a mobile offshore base using five individual units 12, as well as having usable individual units, each individual unit 12 is designed to be three hundred meters in length, one hundred fifty-two meters in breath at the flight deck, and seventy-five point six meters tall. For these dimensions, each lower hull 14 is two hundred seventy meters long, thirty-eight meters wide, and sixteen meters tall, with symetrically faired bow and stern shapes. Depending upon the payload, the transit draft is expected to be between thirteen and fourteen meters. The operational draft is expected to be thirty- eight meters and the survival draft is expected to be thirty-five meters. Special marine connectors 30, seen in Fig. 1, are used to connect the units by means of hinges and/or U-joints. Special connectors are required due to the large loads encountered. Such special connectors are the subject of copending application Serial Number 08/XXX, XXX filed July 31,1997.

Because many varying and differing embodiments may be made within the scope of the inventive concept herein taught and because many modifications may be made in the embodiment herein detailed in accordance with the descriptive requirement of the law, it is to be understood that the details herein are to be interpreted as illustrative and not in a limiting sense.