Davies recently opened up to Doctor Who Magazine (per RadioTimes) about the current status of The War Between The Land and Sea several weeks into its production. The writer stated that, at the time of writing, the series was into its third week of filming in a scheduled singular block of filming that will last until December, but just before Christmas, as opposed to separate blocks, reiterating that writing duties were divided between himself and fellow Doctor Who writer Pete McTighe:

In the office, this show is generally shortened to TWB , which makes me think it stands for Torchwood: Birmingham . We’re in the third week of filming. Very exciting! The shoot will go on until just before Christmas, and it’s a mammoth task, all wrangled by one director, Dylan Holmes Williams. I wrote eps 1 and 5, Pete McTighe wrote eps 2 and 3, and ep 4 is by both of us. Shooting a miniseries as one block brings its own challenges.

Furthermore, Davies admitted that steps had been taken to accommodate the schedules of those involved so that scenes could be filmed more flexibly, rather than sticking to a specific order, highlighting a particular final episode character appearance in the fifth and final episode that would require more flexibility. Check out the rest of what Davies shared below:

Normally, five episodes would be broken down into two or three blocks, filmed roughly in order. But this is all one big block, so an actor could appear for the first time in the very last scene of the very last episode (and indeed, someone does), but we could need them to shoot tomorrow. Equally, someone could be needed in ep 1 sc 1, but maybe we won’t shoot that until December. Logistics galore. When you see all those names listed in the credits, that’s people hammering this into shape, with smoke and steam hissing from the joints as they batter the schedule with big hammers! Production! It’s brutal.