The Army will shrink to its smallest size since before World War II by cutting soldiers from nearly every installation, most notably in two full-sized brigade combat teams with thousands of soldiers each that will become much smaller battalion task forces.

The service provided new details Thursday on how it will eliminate about 40,000 soldiers between now and 2018, falling to an overall size of 450,000 soldiers. The most significant cuts will occur at Fort Benning, Ga., and Joint Base Elmendorf-Richard, Alaska, where the 3rd Brigade Combat Team, 3rd Infantry Division, and the 4th Airborne Brigade Combat Team, 25th Infantry Division, respectively, will be targeted. Each brigade combat team has about 4,000 soldiers, and will be reduced to a battalion of about 1,050, Army officials said.

Fort Benning will drop from 12,655 soldiers to 9,040, and Joint Base Elmendorf-Richardson will drop from 4,603 to 1,895, according to briefing slides released by the Army. Fort Hood in Texas won’t have any brigade combat teams eliminated, but nonetheless will drop from about 37,475 soldiers now to about 34,125.

“The decision to make these cuts is not easy, and will affect just about every Army installation,” said Brig. Gen. Randy George, the Army’s director of force management.

The 2nd Stryker Brigade Combat Team, 25th Infantry Division, of Schofield Barracks in Hawaii, also will face significant change, converting from a mechanized unit using the Army’s Stryker combat vehicle to an infantry unit. Those vehicles will be sent to the Pacific Northwest and incorporated into the Army National Guard’s 81st Armor Brigade Combat Team, saving the active service money.

An additional 17,000 civilian jobs also will be cut across the Army by fall 2018. The service is still determining from where they will come, George said.

The cuts come as the Defense Department pivots following more than a decade of sustained combat operations in Iraq and Afghanistan. The active-duty Army grew dramatically in that time frame, expanding from about 480,000 soldiers in 2001 to a height of 570,000 and 45 brigade combat teams in 2011. But the Army has cut soldiers since, as the Pentagon faces reduced budgets that affect each service.

The Army forecast in budget documents released in February that it would shrink from about 490,000 soldiers to about 450,000 by fall 2018, but said it was crunching numbers to determine how best to it. Significant cuts are also planned at Fort Bliss in Texas (dropping 1,219 soldiers to 25,146), Fort Bragg in North Carolina (cutting 842 soldiers to 38,830) Schofield Barracks (shedding 1,214 soldiers to 14,473) and Fort Stewart in Georgia (down 947 soldiers to 18,457)

Army officials planned to provide details to Congress on Thursday afternoon. Under the plan, the service will shrink to about 475,000 by fall 2016, 460,000 by fall 2017 and 450,000 by fall 2018. It will be left with 30 brigade combat teams and the fewest soldiers it has had since before World War II.

The Army’s force cuts so far have been carried out through a combination of attrition, recruiting fewer new soldiers and requiring some in the Army to separate from the service involuntarily. George left the door open to more of that on Thursday.

“We understand the turbulence this is going to have to our soldiers and their families,” the general said. “This is obviously not a cut we want to make and there are some tough choices at times, but we will minimize that wherever we can.”

Army officials have said that the service can carry out its mission with 450,000 soldiers, but has warned repeatedly that dropping below that would create new risks. If the automatic federal budget reductions — known as sequestration — return, the service could be forced to cut an additional 30,000 soldiers by fall 2019.