They do loads of stuff
You might find this thread from 4 days ago interesting
www.mumsnet.com/Talk/coronavirus/3847823-The-military-are-on-standby
Things the military couid do:
There isn't a contingent of trained medics to redeploy. But there is loads more - the military have a remarkably broad set of skills, and quite a lots of useful kit.
If you want a field hospital, or rapid conversion of a warehouse toma ward, they wouid be the people to do it. They have people with recent PPE experience, not just in terms of BCW personal protection but also some who went to deal with Ebola (there is already provision to call back ex-military who have not yet reached the mandatory retirement age, plus reservists - though if those people are already working in health fields, they may in practice be unavailable)
Other roles: driving tankers and HGVs (including hazardous materials), firefighting, crewing ambulances, some police roles, many engineering roles (probably alongside the regular personnel, not instead of, but a supply of reasonably trained people).
The obvious confounder is that military personnel will be just as susceptible to the virus, and just as likely to need to isolate, as anyone else
One further random idea I had, was that they could staff new decontamination/deeper-than-deep clean units. It wouid be excellent reinforcement of BCW/PPE drills