Sunflower To be fair it's pretty difficult to get to Belgium without going through France from the UK unless you fly. Both the main ports used for the ferry, and the Eurotunnel, are in France. I do the journey regularly back to UK from Brussels where we are based, and I have not yet been able to avoid France or the speed camera just before the Dunkirk ferry exit.
I think you are caught between a rock and a hard place here. I am married to a (now retired) RN Officer who spent lots of time away with his job, plus had hobbies and commitments that were/are not family friendly. I dealt with it before children by doing stacks of over time, and not being about when he expected me to be. Once we had a child, he started a new hobby, that initially didn't impinge as he did one afternoon a week, when the job allowed, but it gradually morphed into weekends, and now weeks away, plus weekends all year round. I decided I could either fight this, or not bother and do stuff with ds. I chose the latter. I have been known to close down anecdotes about his hobby by completely changing the subject or ignoring what he was saying, or sitting there looking bored, or letting them go over my head, and making no comment. He would ask if I was interested, and I'd point out that I wasn't.
I do get pissed off sometimes (but ds went to board in UK at 16 and is now in his third year at uni) when my social calendar and chance of a holiday are arranged round the demands of his current high pressure job and then his hobby, but I use the time to do things I want to do, and a price is exacted from him one way or another, normally in books, sewing stash or shoes.
The thing is that as the kids get older they may be interested in ACF, or you may enjoy the time he is away. The kids may have hobbies/activities that are on the same night as his, so you wouldn't see him anyway. He should be training up his deputy to be able to run at least one evening a month without him, and then up that to once a week. I also agree that the summer camp should be perhaps 9 days (two weekends and the 5 days in between), although I can see why he feels he wants to do both weeks.
You have to ask is it worth breaking up over this, and how much your own children suffer because of this. Yes, they are missing out on time with their Dad, but is that 'suffering'? You could point out to him that they notice he doesn't always spend much time with them, and that this may come back to bite him when they are older.
My perspective is probably different to yours as I knew when we married that the RN would always be first, second and third, so I am used to doing things solo anyway.