The group of retired generals include a former Defense Secretary, a former Joint Chiefs Chair and a White House chief of staff.

The effort is a collective of 30 generals, including six or seven of the most credible Marines that I have ever worked with. He noted that Berger's efforts have already been approved by Congress and the Pentagon, so it is unlikely that they will be stopped now.

The Marine Corps' two-year-old plan represents a fundamental shift in how the Corps trains and goes to war. The Corps has already shifted hundreds of tanks to the Army, helicopter wings have been put in storage, and infantry units are being restructured to become smaller and more mobile.

The changes are part of a broader rethinking of how the military is funded and structured to meet China and Russia, which are challenging post-Cold War U.S. military dominance. It's no surprise that the Corps would struggle with such rapid changes.

A spokesman for Berger declined to comment on the specifics of the retired general's criticisms, but pointed to statements Berger has made to Congress and in public as to why the modernization push is necessary.

Paul Van Riper, a retired lieutenant general who served as head of Marine Corps Combat Development Command, told POLITICO that several generals met with Berger on March 3 to voice their concerns, but walked away dissatisfied that they had been heard.

A former Navy secretary and a Marine Vietnam veteran wrote an opinion piece in The Wall Street Journal that said the talks with Berger were unsuccessful.

Anthony Zinni, a retired general and former head of U.S. Central Command, told POLITICO that the changes Berger is putting forward do not meet the needs of the combatant commander.

In his Wall Street Journal op-ed, he disclosed the existence of the group. Members meet virtually or in-person on a daily basis to plan their way forward and are stepping up their outreach to members of Congress.

The most ambitious modernization effort of any of the armed services is at stake. The armed forces need to train and equip to meet the China challenge according to the National Defense Strategy. In order for the Corps to shift its mission without a massive influx of new funding, tough decisions had to be made. About $3 billion was saved by getting rid of hundreds of tanks and amphibious vehicles.

The equipment that Berger and his supporters say isn't suited for the Pacific fight is tanks and artillery tubes. Modern threats require the U.S. to have long-range precision rockets, small loitering armed drones, and mobile ship-killing missiles that Marines can use to protect U.S. and allied vessels.

Washington's strategic calculations have been changed by the land war against Russia. One of the group's more vocal forward-facing members, a Vietnam vet named Bing West, wrote in a recent article that urban battles in Ukraine and Vietnam show the need for tanks and heavy armor in modern combat. Marines are less capable without them.

Van Riper wrote in the Marine Corps Times that the Corps will have more space experts, cyber warriors, influence specialists, missileers and others with unique skills.

The arguments fail to take into account the changes that China and Russia can bring to the modern battlefield, even if Russia is struggling to use them.

Some experts agree with Berger's plan to change the Marine Corps into a force that can compete with China.

Dakota Wood is a senior research fellow for defense programs at The Heritage Foundation.

The plan at the heart of the fight, dubbed Force Design 2030, has won praise from many members of Congress and leaders from the other services.

The Marines are rapidly replacing cannons with rocket-cannons, and have already warehoused several helicopter squadrons. The Corps' storied infantry units have been transformed into smaller, more technologically dependent units. The retired generals say that the Corps' traditional strengths are being lost because of the moves.

The retired generals want Congress to hold off on Berger's plan because they don't think leaders did enough analysis before getting rid of their tanks.

Van Riper told POLITICO, "Why are you doing this before you have a full understanding of what you want to do?"

Van Riper said that in the past, there would have been war games and field evaluations before drastic moves were made.

The Marine Corps has drafted a rebuttal to the criticisms that meet some of the generals' points. The changes being made to the Corps won't affect its ability to deploy anywhere around the globe, the draft states, and leadership continues to plan for multiple contingencies.

The draft states that tanks are irrelevant despite what is happening in Ukraine today. Major lethality upgrades for our small units have been achieved because of the recommendations made by the Defense Secretary as part of his Close-Combat Lethality Task Force.

The retirees are aware of the changing threats.

This is not a bunch of old guys that don't know what they're talking about.

The Marine Corps stress-tested these ideas for years before Berger took office, through a series of classified war games at the Naval War College in Rhode Island. The games are run by the Navy and the Army.

The latest version, Global 14, took place in November and was overseen by Navy Secretary Carlos Del Toro, Berger and Adm. John Aquilino. The retired generals were not briefed on the full scope of the games because they no longer have security clearances.

The Corps culture is challenged by Berger's plan because it seems to shift its function from offense to defense and trade manpower for technology.

All of the changes had been approved by the Pentagon through the requirements-based system. I'm pretty sure Berger was nominated and confirmed because he had a track record for thinking forward and having vision.

Berger's plan is supported by Congress. Money is still flowing into a variety of new projects, which has been welcomed by defense contractors and lobbyists. Anti-ship missiles, precision-guided rockets and loitering munitions are manufactured by major defense contractors such as Lockheed Martin. The generals have a long shot if they have the factions on board and the restructuring is already underway.

The head of European Command, Gen. Tod Wolters, told the House Armed Services Committee that the new Marine Corps is a brown-water force.

The Marines are working through some of their new concepts during the Cold Response war games taking place in Norway, and they are doing a great job of showing the rest of us how to do it.

The changes did not originate with Berger according to the backers. The Marine Corps is not currently organized, trained and equipped to face a peer adversary in the year 2025.

Neller pointed to the use of electronic warfare, precision weapons, and cyberattacks that would confront Marines on future battlefields against China and Russia.