https://savage.nps.edu/Savage/
The Scenario Authoring and Visualization for Advanced Graphical Environments (SAVAGE) Research Group maintains a large archive of dynamic 3D military models and authoring tools, all open source and built using Extensible 3D (X3D) graphics.
Buildings: https://savage.nps.edu/Savage/#Section8
Environment: https://savage.nps.edu/Savage/#Section10
Ground Vehicles: https://savage.nps.edu/Savage/#Section11
Harbor Equipment: https://savage.nps.edu/Savage/#Section12
Harbors: https://savage.nps.edu/Savage/#Section13
Locations: https://savage.nps.edu/Savage/#Section14
Offshore Structures: https://savage.nps.edu/Savage/#Section16
Ships Cilivian: https://savage.nps.edu/Savage/#Section19
Ships Military: https://savage.nps.edu/Savage/#Section20
Space: https://savage.nps.edu/Savage/#Section21
Submarines: https://savage.nps.edu/Savage/#Section22
Weapons: https://savage.nps.edu/Savage/#Section24