Four stars arrayed in a point-to-center configuration serve as the shoulder rank insignia for Generals (Army, Air Force, and Marine Corps) and Admirals (Navy and Coast Guard). Although five-star ranks still technically exist (and the President has the power to appoint officers to five-star rank at any time), four stars are the de facto highest peacetime military rank in the United States Armed Forces.
In the Marine Corps and Air Force, Generals wear this pin-on metal insignia on both dress uniforms and outerwear garments, while four-star officers in the remaining three branches of the Armed Forces wear it almost exclusively on outerwear and casual garments. Army Generals wear it on the shoulder loops of the Army Green Service Uniform, the Black or Green All-Weather Coat, and the Black or Green Windbreaker (it is also an option for wear on the sleeves of the Blue or White Mess Dress Jacket), while Admirals in the Navy wear it on the Blue Jacket, Black Jacket, Blue All-Weather Coat, and the Khaki Jacket. Coast Guard Admirals wear the insignia on the epaulets of Trench Coats and Windbreakers.
♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦♦
The number of four-star officers in the various branches of the Armed Forces of the United States is determined by Federal statute, with the caps largely determined by the size of the military branch. (There are several factors that affect these maximums, such as assignment to joint duty positions.) Given this fact, it should probably come as no surprise that as of 2017, the Marine Corps, the smallest of the four military branches organized under the Department of Defense, has had only sixty-nine officers promoted to four-star rank despite the fact that it was founded in 1775 just a few months after the Army and a little over a month after the Navy was established.
Just how many active-duty four-star Generals a branch has at any time can vary quite significantly. At the end of Fiscal year 2017, there were a total of eleven Air Force Generals compared to just six in the United States Army, five Admirals in the United States Navy, and two in the Marine Corps. At the start of 2022, on the other hand, those totals had changed to eight in both the United States Army and United States Air Force, six in the Navy had six Admirals, and two in the Marine Corps.