In assuming command of US and Nato forces in Afghanistan, Marine Corps Gen Joseph Dunford becomes the third commander of the International Security Assistance Force (Isaf) in three years. He also may be the last.
Gen Dunford, formerly the assistant commandant of the US Marine Corps, has promised to complete the transition of security duties to Afghan forces and to "set the conditions for an enduring partnership with the Afghan people".
He replaces another Marine: Gen John Allen, who was recently cleared of misconduct after an investigation into "potentially inappropriate" communication with a Florida socialite.
Gen Allen this week said he would retire from the military instead of accepting President Barack Obama's appointment as supreme Nato commander in Europe, citing family health issues.
While Gen Allen was busy finishing his recommendations to the White House on how quickly to withdraw troops from Afghanistan next year, Gen Dunford was studying up and preparing for deployment.
As the second-ranking Marine Corps officer, Gen Dunford has visited Afghanistan many times.
Maren Leed, senior adviser at the Center for Strategic and International Studies, says Gen Allen's departure will not lead to a major revision in the US exit plan from Afghanistan. As it stands now, the US is to finish its mission in Afghanistan by the end of 2014.
"What you will see is [Dunford] spending time building and nurturing relationships, trying to keep morale up, and keep pressure on the Afghan government to make sure that they are progressing and meeting their commitments," she says.
While some Republicans suggest Gen Dunford will be susceptible to political pressure from the White House, Ms Lees says the general rejects this notion.
"Once he is in command, if he perceives that [withdrawal] deadline to be counter-productive or to be too early, he absolutely would make that very clear to the White House," she says.
Gen Dunford earned the nickname "Fighting Joe" in the Iraq war, when he led the initial attack into Iraq and on to Baghdad.
Subsequently, Gen Dunford shot rapidly up the chain of command, faster than almost anyone in recent Marine history.
Afghanistan may prove Gen Dunford's most challenging assignment yet. Ms Leed summarised the tasks ahead:
- finish negotiations on legal framework governing how remaining US forces are treated in Afghanistan
- continue the military campaign
- discuss with Washington the pace and size of the troop withdrawal
- weigh in on the roles and responsibilities of remaining US forces
- keep morale high and troops committed to the mission
The arrival of the war-wise Marine general as the new top Nato commander provides the US with an opportunity to reassure Afghans that while America's longest war is ending, the Americans are not leaving completely anytime soon.