Greater use of part-time reserves and private contractors will be the key to the Army's future, Defence Secretary Philip Hammond is to say.
There will be "difficult" decisions as the size of the regular Army is cut by 20,000 over the coming years, he will acknowledge, with whole units disappearing.
The Defence Secretary will say that the UK's armed forces will need to increasingly operate with other nations in order to continue being able to provide the necessary fighting "teeth".
He will tell an audience of experts at the Royal United Services Institute the future will involve "thinking innovatively about how combat service support is provided" and "using more systematically the skills available in the reserve and from our contractors". It will mean "working closely with partners to operate logistics more rationally through alliance structures" and "looking to others to provide the tail, where Britain is concentrating on providing the teeth".
The changes will involve having to "rethink the way we deliver every aspect of military effect in order to maximise capability at the front line".
Under plans set out in the Strategic Defence and Security Review (SDSR), the Army is to be reduced from 102,000 soldiers to 82,000 by 2020. Mr Hammond will say: "A regular Army of 82,000 will have a different structure to one of 102,000. And some units inevitably will be lost or will merge."
He will add that "the history and the heritage" of some units deliver "tangible military benefits in the modern British Army".
"So there is no question of abandoning the regimental system. But that does not mean that we can avoid difficult decisions as the Army gets smaller. And in making those decisions, the military voice must prevail; ensuring that the Army remains the capable and agile force envisaged in the SDSR."
The changes will also "transform the role of reserve forces", he will say. "The Future Reserves must be structured to provide, as they do today, some niche specialists capabilities that aren't cost-effective to maintain on a full time basis - for example in areas of cyber, medical, or intelligence."
Under the the integrated Army concept, light infantry battalions will be reinforced on deployment through a permanent partnership with reserve battalions.