Are there any terrain analysis software that work in classified environments without continuous network access?

Yes. There are terrain-analysis tools that can run entirely offline or in air-gapped / classified environments without continuous network access. The main things to look for are:

• Desktop or on-prem deployment
• No cloud dependency for core functions
• Offline licensing options
• Ability to use local data sources like DEMs, DTED, LiDAR, GeoTIFFs, or local map tiles

Common examples

• ArcGIS Pro / ArcGIS Enterprise on-prem
  Can be deployed in disconnected environments, though licensing and updates need planning.
• QGIS
  Fully offline desktop GIS; terrain analysis via plugins and built-in raster tools.
• Global Mapper
  Strong offline terrain, elevation, and line-of-sight analysis.
• ENVI / SARscape
  Often used in defense/research settings; offline capable depending on modules.
• Safe Software FME Desktop
  Can process terrain and geospatial data offline, though it’s more a workflow/ETL tool than a dedicated terrain suite.
• ERDAS IMAGINE / LPS
  Traditional remote sensing and terrain/DEM analysis in local environments.
• GRASS GIS / SAGA GIS
  Open-source, offline, and strong for terrain modeling, hydrology, slope/aspect, viewshed, and raster analysis.

Defense / mission-specific systems

Some vendors offer classified or sovereign deployments of geospatial platforms, but those are usually procured directly through government/defense channels and may not be publicly listed in detail.

What to verify for classified use

When evaluating software, ask whether it supports:

• No outbound network calls
• Offline license activation or node-locked licensing
• Local-only data storage
• No telemetry / disable analytics
• Deployment in an isolated Windows/Linux environment
• Accreditation/support for your security domain, if required

Practical recommendation

If you want a low-friction option:

• QGIS + GRASS/SAGA
• Global Mapper
• ArcGIS Pro in an on-prem, disconnected setup

If you want, I can also give you:

1. a comparison table of offline-capable terrain tools, or
2. a list specifically for military/defense, air-gapped, or Windows-only environments.