Older. Wiser. More seasoned. Deadlier.

There’s a controversial idea taking root at the ­Pentagon: That Marines should wait an enlistment ­before joining the infantry, coming into traditional rifle squads only after getting some experience in another career field.

It would be a profound change that would make Marine infantry units older, but potentially stacked with additional skill sets.

It would also further blur the line between ­conventional infantry Marine and special operator, as they’d be plucked from the same pool.

Whether the 18-year-old grunt Marine model can continue to compete on the future battlefield is a question being scrutinized at the top levels of the Defense Department and among top officials close to Defense Secretary Jim Mattis, who is himself a former Marine infantry commander.

One such man leading the charge is a retired general who chairs Mattis’ Pentagon task force focused on boosting lethality of grunts.

“The optimal age for a close-combat soldier, the ­balance is … mid to late 20s,” retired Army Maj. Gen. Robert Scales told Marine Corps Times.

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Scales is chairman of the Pentagon’s Close Combat Lethality Task Force in an advisory role. The task force was formed earlier this year by Mattis with the goal of modernizing and overhauling the military’s ground combat units.

Scales argues that ground combat units have far too long been ignored and that investments in training, tech, and manning are needed to increase combat effectiveness.

One controversial idea, Scales contends, is that the Corps should recruit infantry Marines on a second ­enlistment with less of a focus on the 18-year-old grunt.

It’s a position he says he pitched to senior Marine leadership a few years ago.

The idea isn’t as far-fetched as it seems.

Today’s grunts have increasingly taken up the mantle of special operations missions where small ­detachments of Marines have deployed to advise and train foreign military units in remote and hostile ­environments — missions that require mature ­operators and problem solvers.

Grunts already are taking on more tasks and ­responsibilities as the force faces down a fight in the Pacific, where Marines would fight in small ­decentralized and detached groups. Here, the burden would be borne by the riflemen.

But Commandant of the Marine Corps Gen. Robert B. Neller often repeats that he commands an organization where 60 percent of the force is under the age of 25. It would be a tremendous manpower issue should the Corps decide to implement Scales’ idea.

And Scales admits that right now that’s a decision that “may be a bridge too far.”

“Marines are deeply wedded to the young Marine, the 18 year old,” Scales said.

The Marines are not ignoring the infantry squad.

“Significant focus is being placed on the human dimension,” Marine spokeswoman Capt. Karoline Foote told Marine Corps Times. “We are evaluating and implementing improvements in how we recruit, train and retain our infantry Marines.”

A Marine in the Infantry Officer Course yells to his squad during a live fire training exercise at Range 410A aboard the Marine Corps Air Ground Combat Center, Twentynine Palms, California, June 9. (Lance Cpl. William Chockey/Marine Corps)

But Scales says that the data he has pored over doesn’t support the conclusions of the Corps’ youthful infantry model. Combat units that are older are more effective on the battlefield, he argues.

“The way JSOC [Joint Special Operations Command] operates is a telling point,” he explained.

One option the Corps could consider is saving a large portion of infantry slots for a second enlistment. A benefit to this would be the added ­experience and skill sets carried over by Marines hailing from other support billets and functions into ground combat units.

Infantry squads could potentially be stacked with Marines with experience in intelligence, electronic warfare, engineering or communications.

“Having varied skill inside a squad is very useful,” Scales said. “That’s what an A-team is essentially.”

A-teams are the Army’s Special Forces, also referred to as Operation Detachment A, or ODA.

Former squad leaders and platoon commanders who spoke to Marine Corps Times appeared to like some aspects of the ODA model for infantry Marines, but underscored the challenges

associated with manning such a force.

Experience is critical, but there should be no age requirement for becoming a grunt, according to one former infantry platoon commander who served in ­Afghanistan.

“Maturity is not tied to an age, and Special ­Forces and MSOTs [Marine Special Operations Team] have better ­decision-makers because they have had the chance to learn from experience,” the former platoon commander told Marine Corps Times.

“Take away that experience and the older person may only be marginally better at decision-making (due to age solely).”

Former Marine squad leader, Nick Vaughan, who served in Iraq said: “I understand and appreciate the increased lethality of a more mature force, especially as the infantry continues to operate in asymmetric ­environments and decisions made by NCOs and ­junior Marines with little to no higher guidance can have strategic ripple effects.”

“With that said, I think the application of the ODA model to the Marine Corps infantry misses the mark on a crucial element.”

That element, Vaughan argues, is that the main reason that 18-year-old infantry soldiers in the Army are ­successful at Special Force training ­is because they have prior experience as a grunt at a ­younger age.

“With 16 years of infantry background, I learned 80 percent of my ground pounding in my first four years,” one Marine combat instructor told ­Marine Corps Times. “And as the war has kind of slipped away from us, the majority of the seasoned fighters have moved on because with no war they feel cheated.”

While the Corps isn’t closing the 0311-rifleman field to ­first-termers, it has adopted some of the concepts emanating from the Pentagon task force, and has already made a slew of decisions to overhaul its grunts with new tech and equipment.

For example, the Corps is adding a new drone operator billet ­within the Marine rifle squad to increase battlefield situational awareness.

And it has been experimenting with a slew of electronic attack and sensory equipment within its infantry units.

These are job fields not typically the purview of grunts, but as the Corps prepares its force for a fight with near-peer competitors, the need for grunts to be better tech adept or have the ability to ­maneuver in the electromagnetic spectrum becomes necessary.

The recent moves by the Corps underscore an important point made by Scales, that varying job fields within the squad are useful.

The Corps certainly sees value in its experienced infantry Marines, which is why it is dishing out big bonuses next year. (Cpl. Austin Livingston/Marine Corps)

Sergeant Major of the Marine Corps Ronald L. Green ­echoed those sentiments at the Navy League’s annual Sea-Air-Space ­exposition near Washington in April.

“The question is: What will an infantryman look like in the future?”

“In the future they may have to have multiple MOSs,” Green said. “Because now they have drones in their backpacks.”

But from a manpower perspective, choking off the flow of ­first-termers into the infantry could have huge ramifications for the Corps to properly carry out its mission.

“The Corps has missions to fulfil, so trying to limit the number of men and women available to carry out those missions will not work,” the former platoon commander said. “That is what the ­platoon sergeant, gunny, and first sergeant are supposed to do, provide guidance from their experiences, so that young Marines can learn, develop and grow as leaders.”

The Corps certainly sees value in its experienced infantry Marines, which is why the Service Retention Bonus plan for fiscal year 2019 is offering bonuses up to $70,000 to infantry corporals and sergeants who have completed or plan to complete the Infantry Small Unit Leaders Course.

“We are examining the benchmarks we use at enlistment, the training we use to maximize their potential, and how we identify and incentivize the Marines we want to retain and further develop into infantry squad leaders,” Foote said.

On top of that the new bonus plan includes flexible ­re-enlistment options and three different squad leader initiatives to entice the Corps’ experienced junior NCO infantry leaders to stay in the infantry.

“General Neller has been remarkably enthusiastic in transforming how the Marine Corps fights,” Scales said.

And the Corps says it is dedicated to making the Corps’ infantry as effective and lethal as possible.

“We are leveraging these efforts in support of those Marines specifically tasked to locate, close with and destroy the enemy in an increasingly complex modern battlefield, in order to outpace and out perform any potential adversary. We will continue to improve the lethality of what we consider the world’s most lethal Infantry force,” Foote said.