Combat in Military Bands
It's been a number of years since I retired, but I'm reasonably plugged into what's going on in the Army, in particular, but deployments to combat zones are a fact for Army line bands and, on more rare occasions, for the Major Command bands such as the Training and Doctrine Command Band (now at Ft. Eustis, VA); Forces Command Band (Ft. Bragg, NC); and the US Army Europe Band (Heidelberg, Germany). The Army Field Band has been to Baghdad according to their web site, but I would not characterize that service as a deployment.
Deployment durations vary anywhere from a few months to a year, depending on the need, tactical situation, and political considerations. I would think that with the political developments in Afghanistan, deployment of bands to that area will probably drop off to some level, but will, of course, continue as long as there's a military presence in that country. Iraq deployments no longer occur as the mission there has been declared "complete".
The Army has gravitated in theory and, at least to some level in practice, toward what they call "performance teams" and these teams, rather than an entire band, are designed for deployment. The theory goes, bands subjected to more deployment opportunity (this is debatable, but let's say for the sake of illustration the 101st Airborne Division at Ft. Campbell) will have more "performance teams" of various sizes and configurations since that band would likely deploy more of its teams.
Clearly, the Army wants to send performance teams that provide the type of music that is most needed, and that includes smaller ensembles such as jazz combos, brass quintets, woodwind quintets, and the like, in addition to the larger ensembles such as the stage (big) band and the concert band.
Bottom line is, there is no "magic" formula about deployment. If you're there and you're ordered to go, you go. Most musicians I've talked to who are second term and beyond have deployed at least once and some have deployed two or more times.
To the best of my knowledge, no Army bandsman has been killed in combat operations since Iraq and Afghanistan operations started in 2001 (bands started deploying to Iraq in 2003). That is not to suggest there haven't been dicey situations like IEDs and the like that bandsmen haven't had to deal with in some form.
Here's a link for more information, though it's a bit dated:
http://www.almc.army.mil/alog/issues/May-June10/army_bands.html
I hope this helps answer some of your questions.
U.S. Army, Retired (built mid-1950s)
Adams E2 Euph (built 2017)
Boosey & Co. Imperial Euph (built 1941)
Edwards B454 Bass Trombone (built 2012)
Boosey & Hawkes Imperial Eb tuba (built 1958)
Kanstul 33-T lBBb tuba (built 2010)