The author writes "I do not foresee any smartphone app ever being approved for this purpose." (the purpose is 'passing classified information for military operations'), while in fact, I'm not sure I see the issue - all the app (any one of them, including WhatsApp, Signal, etc.) needs to add is what is referred to as 'conditional access' to some chats. Meaning, you can define chats as only authorized for users whose identity is provided by a trusted Identity Provider, or are running on certified devices. This type of security is already implemented in many enterprises, supported by browsers (to some extent, at least), and can be relatively easily be supported by applications. Custom made chat apps already use this (e.g. Workplace Chat, which is used by Meta), and so I'm not sure it's something we won't see supported by other commercial apps messaging apps.
What he means by "I do not foresee any smartphone app ever being approved for this purpose." is that a commodity smart phone is an insecure platform, so the military will not be approving any app designed for a commodity smart phone.
And by insecure here, he and I mean that its not a platform designed and manufactured to meet the large number of requirements for handing classified information. It may be secure in the sense of industry standards or conventions, but its not secure in the sense of military information security.
If I read it correctly it's because they think phones are a no-go from the outset, so clearly apps for those phones are out, too:
> When government and military officials want to discuss operations, they’re typically required to go into a SCIF (Sensitive Compartmented Information Facility), which ensures:
>
> - That they are not being wiretapped. (To this end, mobile phones are not permitted in a SCIF.)
Whether this is actually true or not I wouldn't know and can't be arsed to research, but it makes sense to me. Whether it's reasonable to assume based on this that phones are completely out I also don't know.
