The office was empty between 1845 and 1848, the bishop of Zagreb acted as procurator. After the events of 1848 March 15 for the Court it became important to assign a new bán who is loyal to the Austrian government, before the Hungarian government is set up - which would be independent and responsible towards the Hungarian Parliament-, and the Croatian bán would be subordinate and - god forbid - loyal to them, for they could handpick the person for the job. The choice fall onto colonel Josip Jellacic, an imperial officer, who was the commander of the first border guard grenzer regiment at the time, and spent over two decade in his majesty's service. His name was put forward by the Austrian minister-president, the Czech born Kolowrat. Since the border region was under military control, as the regiment commander he was the administrator of civilian affairs too, eg. responsible for building roads. He did a good job gaining the confidence of the population, and became respected among them.
On March 23 he was appointed as the new bán by king Ferdinand V. - on the same day the new Hungarian government started to form - so he gained control over the military affairs of Croatia, and then on April 7-8, they bumped his rank up to lieutenant fieldmarshall, to became the leader of all the military of the emperor and king there. If I understand correctly Croatia had it's own military, then the bán had own regiments - one if which Jelacic was the colonel of -, there were the border guard units, and other units which were either imperial Austrian, or belonged to the Hungarian king. But however it was precisely, the fact of the matter is that he became the leader of all essentially, and he had utmost loyalty to the emperor and his bureaucracy. They also successfully prevented the spread of revolutionary movement into the border regions.