Remaining in the army after WWII

It may depend on whether he enlisted or was drafted. If he's "regular army" as opposed to being a draftee, then he would stay through his enlistment and be able to reenlist as normal. The military mustered out the draftees first to get back down to a more "normal" (read sustainable) level.

If he stays in, the first place he would probably be assigned after the war is Southern Germany in the American Zone of Occupation. There he would be doing things like refugee control, POW camp duty, and rebuilding the old German Army Camps for occupation by U.S. Soldiers (which we still use today). Also, some of the U.S. Soldiers occupied Austria (which was also divided between the allies for a while).

He would be required to take a physical fitness test twice a year and to get a medical physical once a year. Having been wounded, esp. with shrapnel, they would be paying particular attention to that region during the physicals. Remember, since the Army was reducing in size, he'd have to be sure not to show any signs of lingering damage to stay in - After all, Audie Murphy got booted due to injuries and he was the highest decorated soldier in the war.

Majors do not have much pull. They are the lowest grade of field officer. I'm assuming your soldier is an enlisted man, which means he's not going to have a lot of contact with officers (outside of very directed encounters - "Sergeant, take your squad and move them to Coordinates X and take out that enemy pillbox. That's all."). The Army is a very hierarchical organization (and very caste oriented). NCOs did not fraternize with their enlisted and officers did not fraternize with NCOs or enlisted.

Now, however, if your soldier was wounded saving the life of an officer and you want him to "help out" - one, the soldier would probably have been put in for some kind of award and two, that officer might recommend the soldier for a battlefield commission (if he was already in a position of responsibility). As a decorated hero, his recommendation for commission might be taken more seriously. Then as a newly minted officer, the assignment to the Pentagon would be more realistic (the major might recommend him to his uncle, the General). Remember, at the Pentagon, unless you're a full colonel or above, you're more or less a non-entity. A lieutenant is as invisible as a private there.

Not quite your scenario, but, my brother in law came out of WWII as a Sergeant (not sure what level). Never wounded. He went from regular army to army reserves and stayed in for twenty years and was a full colonel when he retired. He was able to go wherever his 9-5 job took him - just went to summer camp annually and some reserve meetings. Plus, he did a lot of army coursework while he was in the reserves. Puma

After the war ended everybody "wanted the boys to come home" so there was a huge demobilization. They shipped people stateside and discharged them as fast as possible. The priority for discharge was based on "points." You got points for length of service, combat duty, any medals or awards received, etc. The more points, the quicker you got sent home to be discharged.

Look into "Operation magic carpet." They pressed aircraft carriers into service as transports and loaded them full of troops to get soldiers back to the states faster.

Someone who enlisted in '42, saw combat, was wounded, and possibly was awarded a medal, would likely be a "high point bastard" and would likely be in one of the early groups to be discharged.

The Army of Occupation in Germany was renamed "The Constabularly". It was largely made up of guys who were drafted near the end of the war or even after it ended as the longer serving guys were mainly discharged by then.

Your character could have voluntarily reenlisted in the army when he was to be discharged. He'd have to have a good record and be able to meet physical standards.

As far as him making Captain, the jump from enlisted to officer is hard, but not impossible. One very likely and realistic way would be for him to be nominated for either a direct commisison (2nd Lt) for his proven leadership skills before the war ended or for him to be entered into an officer training class, conducted in Europe, that would commission him as a 2nd Lt after completion of the class.

Your Major could have nominated him for either one.

If he's a 2nd Lt at the end of 1945, he might very well make Captain by 1949.

Don't forget that the Korean War was right around the corner starting in 1950. A lot of Officers who thought they were done with the Army were recalled to serve in Korea in 1950. I'm not talking National Guard or Army Reserve officers, but ones who were discharged at the end of WWII and didn't join the Guard or Reserves, didn't go to drill in that time, and thought they were "out for good." If you are in officer they can call you back, and that's exactly what happened to a lot of WWII officers in 1950.