I don't mean to put a downer on the situation, but make sure this is really what you want before going for it. And make sure they really understand the stresses involved and how lonely it could end up being for them.
The reason I say this is because I have two examples, one short term, one long term.
First is a mate of mine expecting to go into the RAF and get every weekend off to go home and see his missus, except the flight he was a part of kept screwing up and their weekend leave was being revoked. This was just during their training. The few weekends he did get leave he decided to stay at Halton to study. The one weekend he did get off she was away on a hen weekend and they didn't see each other.
Needless to say things went down hill pretty sharpish which affected his next phase of training. End result was he walked away from his trade training to try and save his relationship of 6 years (and they were strong before, not ever spending more than a few days apart) and it still went to pot, no job and no girlfriend.
The second is my girlfriends brother who is in the Navy. He goes away on 13 week tours with no communication whatsoever for pretty much the duration. No Skype, no messaging, no nothing. They've been together for 15 years, and met in the Navy, so she knew what she was getting herself into from the start. But his last tour really took it's toll. She heard from girlfriends of his mates that he had got his Chiefs whilst away, so she drove herself mad thinking about having to move to Pompey from Scotland and having just bought a new house and the kids settling into a new school, her finding a new job, it just all got too much for her. She couldn't cope, and this is someone who has dealt with it all for 15 years. It has crippled them and they are having to sort it all out and consider their options about what to do next.
All I'm saying is make sure you know you can handle it, and plan what you'll do if you realise things are heading south. Sit your missus down and explain that this is just the beginning of a long road in the forces and things can and will change meaning they may get pulled from pillar to post. And make sure they have a good support network around them, friends and family, to help out if things get a bit rough.
I know everyone's circumstances are different, but it's better to be prepared than not.
It's them that make the sacrifices in my mind, we move where the job needs is, they're the ones who follow and have to settle again somewhere new, or look after kids while we're away, or have to break the bad news to us when we get back that something awful has happened.
I just think they deserve fair warning of what they are letting themselves in for lol.
Sorry to be so downhearted on a Monday morning haha