Who writes what for the European defence industries?

Big industries. Big question. The subject probably deserves an extensive survey. For the moment, all I can offer is a few observations.
Please feel free to comment or correct.

Observation #1: European defence contractors based in the UK work only in English and most others in their national language plus English. Some work in three or four languages, the selection always including English.

Observation #2: Many higher-level documents are, as far as I can tell, drafted by engineers and other categories who do not see themselves primarily as technical communicators. Some higher-level documents are, I presume, drafted by people  who do see themselves primarily as technical communicators.

Observation #3:   Technical documents accompanying products are, as far as I can tell, generally produced by specialised tech doc contractors employing technical writers and translators who, again, as far as I can judge, are seldom members of organisations representing their profession.

Observation #4: A great deal of 'front-line' documentation  is, as far as I can tell, drafted by engineers and other categories who do not see themselves primarily as technical communicators.
Some 'front-line' documentation is produced by corporate and technical journalists, whether employees, freelancers or subcontractors.

What do I mean by the term 'front-line' documentation?  This category includes websites, documents available to customers, prospective customers and other interested persons via websites. Also hardcopy documents distributed at trade shows and the like. Press releases, presskits, brochures, product datasheets, company magazines and in-house publications are all examples, along with technical journalism article for trade publications.
Virtually all 'front-line' documentation drafted in a language other than English is translated or adapted into English.

What do I mean by 'higher-level' documents? This category includes 'front-line' documentation, but is broader as it also includes various types of in-house and published documents. I'm sorry if that's not very clear. The best I can do for the moment is to list some examples: speeches, policy statements, marketing discussion documents, in-house language resource documents (éléments de language), executive summaries of bids and documents serving as input for all of the above.
Many 'higher-level' documents   drafted in a language other than English are translated or adapted into English.