This question comes up frequently. In doing some research for ship models on my layout I came across this US Navy document. It is interesting. Note the lack of styrene as an acceptable material.  Also gives you an idea why government contracts are so expensive, note the documentation section.

Although only a few materials are prohibited in "Specifications for Construction of Exhibition Models of U.S Naval Vessels," some recently developed model-building materials and techniques should be avoided until sufficient time has passed to properly evaluate their longevity. Though some of these recently introduced materials may ultimately test superior to more traditional techniques, substances of unproven longevity should not be employed in models built under these specifications. It is advised that fiberglass resins, styrene, expanding foams, casting resins, and cyanoacrylate glues be avoided when other materials can possibly be used. 

Workmanship 

Workmanship shall be in accordance, in every respect, with the best model-building practices. Hulls shall be smooth, fair, and symmetrical; without blemishes, sap pockets, or tool marks, and shall be scraped and sand-papered to smooth surface. Machined parts shall bear no tool marks. Castings shall bear no visible mold marks. In no case shall glue alone be deemed sufficient to hold deck houses, fittings, or other appurtenances in place. Mechanical fastenings such as screws and pins shall be used in addition to adhesives. 

Range 

Models shall be museum quality and shall consist of the whole exterior of the vessel from keel and appendages to the top of the highest antenna or fitting, and shall include interiors of such enclosures, conning stations, deck house topside stations, gun and missile stations, hangars and bays as are accessible to weather without opening watertight doors or ports. Generally, all items on the prototype twelve inches or larger for 1:96 scale (six inches or larger for 1:48 scale) will be reproduced. 

Rigging. 

Running and standing rigging and cable antennas shall be represented. Windlasses shall be wound with appropriate cable or line. 

Ports and Windows 

Large windows shall be indicated on the model by clear acrylic plastic. Ports shall be transparent, and shall have a hole bored behind them to give an appearance of depth. 

Gun Turrets 

Gun turrets shall have the openings in face plates required for elevation of the guns. Where required, gun shrouds shall be represented. 

Aircraft and Vehicles 

Where appropriate for the mission of the actual vessel, and visible on the model, scale aircraft or vehicles will be provided. Landing pads shall be provided with at least one representative scale aircraft. 

Small Boats 

Small boats shall be mounted on davits or otherwise as actually carried and shall show all details, motors, and equipment twelve inches or larger in actual size. If represented with weather covers, gripes and all fastenings visible are to be shown. Landing craft and whale boats shall be without covers and shall show all exposed details and equipment. 

Special Features 

Special functional features peculiar to the vessel (for example: stern doors, towing devices, special antennas, fire fighting gear, etc.) shall be shown. 

2. MATERIALS 

Rigging 

Layed rope shall be represented with first-quality, twisted, linen line. Wire cable will be used to represent wire cable. Wire will be used to represent wire. Care shall be given to insure the proper color of all rigging. Knots and seizings may be secured with thinned white glue. 

Flags 

Flags shall be such material that a natural appearance as in a calm is achieved. 

Deck Covering 

Deck covering shall be represented as installed on the vessel, including safety treads and nonskid areas. Decks which are bright shall show planking, seams, scarfs, butts, and miters, and shall be rubbed to a dull finish. Paper shall not be used to represent deck coverings. 

Hull 

Hulls shall be built up in lifts of clear, first-grade mahogany or basswood; doweled and glued together with water-resistant glue. The wood shall be completely free of knots, checks, and sap pockets and shall be thoroughly seasoned. Models over 12 inches beam must be hollowed for reduction of weight The hull shall be composed of the least number of parts necessary to achieve the proper shape. An excessive number of glue joints shall be avoided. On models less than 12 inches beam, hull lifts shall be cut to the full body shape: lifts shall not be cut in halves, thereby creating a glue seam along the vertical centerline of the model. The lifts shall conform accurately to lines of the vessel as shown by the plans. A stable, durable, flexible body putty may be used in moderation to fill gaps. 

Hull Inspection 

Prior to applying any sealer or primer to the hull, the hull shall, at the builder's expense, be crated and sent to the Curator of Models, Code 301, Naval Surface Warfare Center, Carderock Division, West Bethesda, Maryland 20817-5700 for inspection and testing. 

The Curator of Models will inspect the hull for wood-type, grain, seasoning, putty, glue-type, checks, excessive glue joints, and conformity to plans. Samples of wood, glue, and glued pieces may also be required for destructive tests. The Curator of Models shall return the hull, collect freight, as certification of compliance. 

Hull Fittings 

Propeller shafts, struts, bearings, bilge keels, etc. will be made from brass, aluminum, or stainless steel. 

Propellers 

Propellers should be cast in bronze. If another material is used it shall first be copper plated and then brass plated. Plastic propellers are not permitted. 

Ship Fittings 

Fittings and accessories shall be of metal or other suitable material which will permanently hold its shape and will not deteriorate from temperature, humidity, light or chemical reaction with other parts, paint, or the atmosphere. Lead or lead-bearing compounds are not suitable for any component. No ferrous materials shall be used. 

Masts, Antenna Masts, Yardarms, etc. 

All masts, antenna masts, shafts, yardarms, booms, etc. less than 3/16" diameter shall be metal. 

Solder 

All solder points shall be silver soldered wherever possible. 

4. INSPECTION 

Beyond the hull inspection required in section 2., the model may be inspected by the Curator of Models or his designate during construction and upon completion at the contractor's plant. 

5. DELIVERY 

Schedule of Materials 

The contractor shall provide, at the time of delivery of the model, a schedule of materials and brand-name products employed in the construction of the model. The schedule of materials will be added to the historical file retained for each model. 

Sample Schedule of Materials. The schedule of materials written in tabular form by the contractor should include, but is not limited to, the following data: A. Type of wood used for hull. B. Type of wood filler used. Include brand name. C. Type of primer used. Include brand name. D. All paints used. Include brand name and color designation. E. All glues used. Include brand and areas where employed. F. Any other significant materials. Include clear sprays, stains, waxes, and the types and application areas of any sheet, cast, foam, or resinous plastics (if any). 

Transportation 

The contractor shall be responsible for delivery of the model and exhibition case in good condition to the location designated in the contract. 

Deviations 

Desired deviations, if any, from these specifications will be enumerated on a case-by-case basis through the normal contract process. 

Model specifications are published here for general interest and are not to be referenced regarding official Navy contracts.