Augustus did not immediately put into effect all his suggestions, fearing to meet with failure at some point if he purposed to change the ways of all mankind at a stroke; but he introduced some reforms at the moment and some at a later time, leaving still others for those to effect who should subsequently hold the principate [Roman History, 52.41.1-2].
Dio was one of the first to attribute to Augustus a general policy of reform that encompassed almost every field of the administration, and in many books on Roman history, the chapter after the civil wars is devoted to Augustus and the Augustan system. Of course the authors know better, but the structure of their books makes it easy to overestimate the importance of Augustus.
To the army, the reforms of Claudius must have been just as important. Many aspects of the military changed considerably in the early forties, and even if we have certainty about only a couple of them, the general picture is reasonably clear:
- The layout of forts changed.
- The Mainz swords were replaced by Pompeii swords; there were changes to the shields; the bronze Coolus helmet was replaced with the Imperial-Gallic type.
- The auxiliaries were reorganized; terms of service became standardized; from now on, citizenship (and diplomas) were given to those who were demobilized.
- Along the Rhine, the limes was created – buildings have stone foundations, the Classis Germanica was organized, watchtowers erected.
- The careers of the officers changed.
Some of this is controversial, but it is interesting, and a useful antidote against attributing everything to Augustus. You can read more about the reforms, and some caveats, here.
C. Thomas, “Claudius and the Roman Army Reforms”, in: Historia 53 (2004)