Dowding, a former Harlequins rugby league player, will again be registered with Bridgend in the Welsh Premiership but he will train with the Ospreys B team.
The 26-year-old plays for the Army and he has served in both Iraq and Afghanistan with 7 Para RHA.
Dowding moved from the back row after losing weight during a tour of duty in Afghanistan and his front row potential was spotted by army colleague and former Scotland prop Mattie Stewart.
"The army has given me some fantastic experiences - not least travelling the world to play rugby," said Dowding.
"There's no getting away from it - I have experienced plenty of things in places like the Iraq war and in Afghanistan that aren't so fantastic.
"But I'm really fortunate to have been able to experience everything that I have done and now I have a great opportunity to play rugby, training with the Ospreys and who knows where it will lead?
"The way it works with the army is that you can only sign a contract with a rugby club for 12 months at a time as they review things annually.
"I'm still a serving member of the army and could be called up if the regiment is, and I will be serving my full 25-year term.
"There are a couple of other players combining an army career with playing top-level rugby, so it is achievable.
"It's a massive opportunity for me, particularly with us having props away in the Wales squad."
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