I enlisted in 1976 and it wasn't good then either LOL. A military does not fly apart over night and in Feb 77 when I got to the ship it was a mess. When I left in Oct 80 things had changed quite a bit. Don't get me wrong Carter was a dunce I voted for Ford myself. But Carter addressed the military decline at least Navy wise and I remember the changes taking place and they were positive ones.
When I got there we had dysfunctional dress blues unsuitable for storage on ship especially for enlisted. They were an officers uniform variant actually that came out sometime in the 1970's not sure who did it but bad idea. The more functional and traditional Crackerjacks came back under Carter not Reagan. I know because for muster out sea-bag inspection I had to buy them.
Such things as the Bosuns whistle which were not heard in 1977 were used again on every ship. This is how morale was addressed. Lifers were asked to volunteer to come back and straighten the mess out. My last chief was one of them. Traditions were restored with that came a rise in morale to follow.
Retention became a serious issue and in 1980 $15,000 and next rank was a pretty good deal but E-4's and below who were married were still having it rough. The rampant AWOLs and desertion for a discharge after 30 days issue was resolved and here's how. You walked and they found you. Once found you faced a Court Martial. You were awarded brig time {usually 90 days} and a BCD. But it did not end there. The bad time was tacked on to your service obligation and they made certain every day was served that the person agreed to. Again that began under Carter. Reagan was handed a military on the mend because of it. It still had issues but positive change was made likely because of the Iranian crisis. Other than that I can not name you one other single thing James Earl Carter did right as POTUS.
I spent 8 years in the USN [1965-1972], including a year in Vietnam and another 8 months off the coast. The biggest change that happened in the military was the elimination of the draft and all volunteer force, which was put into effect by Nixon in July 1973. This was the source for the resurection of the military. Carter was the beneficiary. Reagan then provided the funds to rebuild it. You give Carter far too much credit.
Those were another brainchild of our infamous Adm Elmo Zumalt.