Title: It Happened Here (1965)  released by Milestone films DVD
Directed and produced by Kevin Brownlow
Runtime: 1:36:24

IMDb:  tt0055024

Those who have seen the  torrent called "Winstanley" by Kevin Brownlow
will enjoy this first effort by Brownlow and Andrew Mollon.

Excerpted from the Wiki:

The film was directed by Kevin Brownlow, who later became a prominent film
historian, and Andrew Mollo, who was to become a leading military historian.
Brownlow developed the concept of the film when he was eighteen, in 1956. He
turned to Mollo, a sixteen-year-old history buff, to help him with the
design of costumes and sets. Mollo was intrigued by the project, and became
his collaborator.

The film was in the making for the next eight years, which the Guinness Book
of World Records (as of 2003) calls the longest ever production schedule. It
was shot in black and white on 16 mm film, giving it a grainy, newsreel
feel. The audio quality (and lighting) on the opening reel is rather poor,
which makes the dialog difficult to follow for the first few minutes. It had
a cast of hundreds, all volunteers, with only two professional actors among
them (Sebastian Shaw, Reginald Marsh). (A number of the extras in the film
were members of British science fiction fandom, and a portion was previewed
at a science fiction convention in Peterborough.   End excerpt.

My notes

 Using volunteers in the manner that Peter Watkins does drew me to this
film.  It is similar to "The War Game" and "Colloden."  My local library had
purchased it but at the time I knew nothing of Brownlow until the re-release
of Winstanley (2009).

   There is a companion book published called "How It Happened Here" a
picture of the book cover is included.

 Though not a do it yourself effort in the practical sense of the term, "It
Happened Here" shows what can be done with minimal production equipment.  
The subject of occupation is current.  A comparison of "It Happened Here"
with the recent television series "Jericho" is recommended.

  A further exploration of how "newsreel" footage was used in the depiction
of war is in "The Victors" (1963)  by Carl Foreman  and currently available
on torrents.  For me it is quite telling the difference between what
Hollywood stars did in "The Victors" as compared with any crop of Young
Lions today.  It's not only telling, it's disheartening.  "The Victors" is
one of the great anti-war films.

Notes written January 7th, 2013

 New notes written  June 14th, 2020

Some alternate cover art