Abdullah's promotion of Prince Miteb bin Abdullah was widely seen as part of the monarch's effort to elevate a new generation of royal princes to command positions to lead the kingdom through the dramatic changes sweeping the Middle East.
The king has made several key leadership changes in recent months which clearly will affect the increasingly pressing issue of the royal succession, given Abdullah's age -- he'll be 90 this year -- and the infirmity of the crown prince and others of his generation, the son's of Saudi Arabia's founder, King Abdul Aziz.
How this will play out isn't altogether clear.
But given the advanced age of Abdullah's generation, who have handed the throne from brother to brother rather than from father to son since Abdul Azia died in 1953, the point at which his grandsons take over is fast approaching.
The king created the Ministry of the National Guard by royal decree, thus augmenting the importance of that force, which Abdullah himself had commanded from 1962 to 2010 when he put Miteb in charge.
This is the second major shuffle within the military realm he has made within a few weeks and would suggest he is seeking to assert direct control over the kingdom's armed forces.
Miteb's appointment follows Abdullah's surprise dismissal of Prince Khalid bin Sultan as deputy defense minister, a post that effectively runs Saudi Arabia's regular armed forces and which he had held since 2001.
Khalid, who commanded all Arab and Muslim forces during the U.S.-led Operation Desert Storm in the 1990-91 Gulf War against Iraq, was widely considered to be a competent administrator but lacking in military skills.
He was widely blamed for the poor performance of Saudi forces, and their heavy casualties, against rebel Houthi tribesmen in northern Yemen in 2009, the largest Saudi military operation since Desert Storm.
Khalid, 63, was replaced by a relatively unknown royal, Prince Fahd bin Abdullah, a former navy commander.
Among Abdullah's generation of Saudi princes jostling to succeed him, Khalid's credentials and strong family clan within the House of Saud put him among the leading candidates.
His father, Crown Prince Sultan, who was defense minister for nearly five decades until his death in 2011, was immensely powerful and ensured that despite his military shortcomings the son held a senior position that would boost his prospects when it came to choosing a new monarch.
The appointments of Prince Fahd and Prince Miteb thus give the king immense control over Saudi Arabia's military, the regular armed forces run by the Defense Ministry, and the National Guard, a largely tribal and conservative force whose primary mission is to protect the House of Saud and act as a counterbalance to the regular military.
The current defense minister, Prince Salman, Khalid's uncle and the crown prince, is in poor health and is reportedly to be suffering increasingly from dementia.
So Fahd, Abdullah's man, effectively has hands-on control of the vast defense budget and Saudi Arabia's regular armed forces and is likely to eventually take over as defense minister himself.
"Prince Fahd's pedigree is not part of the House of Saud's mainstream. So he's not a potential future king," observed Simon Henderson, director of the Gulf and Energy Policy Program at the Washington Institute for Near East Policy.
"But Khalid's sacking will likely be seen as a setback for some of the king's rival half-brothers -- the so-called Sudairi princes -- and their sons," said Henderson, a longtime observer of Saudi affairs.
"Ironically, the new deputy defense minister is distantly related to the Sudairis," the seven sons of Abdul Aziz's favorite wife, Hassa al-Sudairi who have long formed a powerful and often dominant faction within the royal family.
"For Washington, Fahd's appointment means that the U.S. military now has a competent, experienced and authoritative royal to deal with in further developing the long-standing bilateral relationship," Henderson noted.
"But Washington should also be concerned that this latest twist in royal politics could provoke destabilizing countermoves within the House of Saud," Henderson observed.