One striking image shows the Marine Corps generals who will have left the Trump administration, after the president praised their service

• President Donald Trump once boasted that his administration was staffed by notable members of the US armed forces.
• Those service members will soon be leaving his administration.
• The latest former Marine Corps general who will have voluntarily left the administration is Defense Secretary Jim Mattis.

US Defense Secretary Jim Mattis' upcoming departure from the Trump administration was largely expected in the near term, but his official resignation letter on Thursday still shook Washington, DC, and caught defense officials and lawmakers off guard.

The news follows a series of departures from high-profile military generals in the White House, namely Marines who have served with distinction throughout the wars in Afghanistan and Iraq. Many of these Marines have now left the Trump White House amid numerous reports of disagreements or criticisms of Trump.

The photo above, taken in 2013, marked the first time six four-star Marines Corps generals were actively serving in the Marines.

• Jim Mattis, the Secretary of Defense, announced his resignation on Thursday and is expected to leave the Pentagon at the end of February. Mattis was a four-star general who led the US Central Command and was celebrated as a top choice to lead the world's most powerful military. Mattis cited his disagreements with Trump's policies as the reason for his decision to resign as the highest-ranking service member from the Defense Department.
• John Kelly, the former White House chief of staff, was a four-star Marine Corps general who once led the US Southern Command. He served as secretary of the Department of Homeland Security before being selected by Trump as his chief of staff. During a rocky tenure during which he had been expected to bring order to a chaotic West Wing, Kelly faced headwinds, and sometimes clashed with Trump on a number of issues.
• Joseph Dunford, the chairman of the Joint Chiefs of Staff, served as the commandant of the Marine Corps and the International Security Assistance Force in Afghanistan. His term as the top commander of the entire US military ends in September 2019. Trump announced US Army chief of staff Gen. Mark Milley as his replacement, despite some reports of concerns from Mattis.
• John Allen, the former commander of the US-led coalition in Afghanistan, did not serve in the Trump administration. Instead, he was an outspoken critic of Trump throughout his campaign and presidency. During a speech at the Democratic National Convention in 2016, Allen endorsed Hillary Clinton and likened Trump's presidency to a "business transaction" that conducts "illegal activities." Trump fired back at Allen through a tweet and said his fight against ISIS "failed badly."

The circumstances of the officers' various exits may vary, but Trump's generals - service members he spoke highly of throughout his campaign and the early days of his presidency - have now left an apparent void in the White House.

In addition to the Marines who will have left the Trump administration, US Army three-star general H.R. McMaster, Trump's former national security adviser, was fired in March. His tenure was marked by numerous reports of disagreements with Trump, who once described him as "a man of tremendous talent and tremendous experience."

McMaster replaced another US Army three-star general as national security adviser, Gen. Michael Flynn, who was fired after he was discovered to have lied to the FBI and senior White House officials about his communications with Russians officials.