Encrypted freq hopping wide spectrum dynamic power radios with encrypted repeaters managed by the military on the field is the only semi-secure option and even that comes with significant risks. Even then there should be little to no voice comms. Just a 4 byte group designation and a 2 byte code burst that maps to per-arranged tactical instructions and optional coordinates. Ack codes should be optional in the event the enemy gets the decryption key of the hour. Manual ack should have the option of commands received or squad compromised.
XMPP has signal style encryption with OMEMO now. Just use that.
Personally I'll stick to Wire, Threema, and my own Matrix server instance.
Forget metadata being protected. Though imo Telegram is great for any communication that does not need to be secret.
People have also expressed concern about flaws in the custom protocol used, though most of the concerns are related to metadata leaks than actual text message communication, which might be ok or not ok depending on your threat.
it is becoming very funny at this point
