The Department of National Defence would have all the same responsibilities as a typical custodian or tenant to the degree that they're in a building that they are renting via Public Works. What is different about them, though, is that much of what they hold is special purpose space, i.e., not office space. So there is, I would say, a different level of engagement between departmental officials and the maintenance of special purpose space. It usually requires a much more unique type of expertise, typically a more hands-on management style.
Other departments that would have the same kind of challenge might be departments that have an ops centre. DND does, but so does Public Safety and Emergency Preparedness, RCMP, etc. The degree to which the property is specialized has an impact.
As well, there are thresholds above and below which ministers are authorized to operate. I would venture to say, and we can check the details for you here, that DND may have a higher threshold than, for example, a minister who or a department that is not a particularly big player in the property business.