Too many narcs on the ham bands would track you down for operating encrypted ham packet radio. You're better off using something like LoRa over the ISM bands. Build out a network of hidden mesh nodes over the area you'd like to operate and that's probably the closest you'll get to a true clandestine network. Of course the major issue with transmitting any RF energy is that someone can watch the spectrum and look for those transmissions and eventually track down your nodes. LoRa uses DSSS which if operating at minimum power, could help hide transmissions.

If you want to add some illegality to the system, you could piggyback on amsats or open relay satellites like FLTSATCOM to expand your network and hide better.

Isn't ham radio no-encryption-allowed, no-commercial-use-allowed?

Ham radio is actively unfit for the requirement of "clandestine" for the parent commentor's purpose.