Absolutely. It's a deployment, not a standard tour at some installation on PCS orders. Could be a month or two or, it could be a year. Units are rotated into a combat zone, not individuals anymore, like Vietnam. The Repo Depots went out (thankfully) a long, long time ago. The end date of a unit deployment is generally at the discretion of the theater commander (I think
).
Our tour lengths are set IIRC by Big Army. The whole "not to exceed XXX days".
When I got sent to Iraq in 2003 we left on six month deployment orders...which got extended to 12 months. At one point during the surge units were there for 15 months. Afghanistan was 12 months though the Army has cut tours back to 9 to save money on sending people home on mid tour leave.
Marines have been 7 month tours for both combat zones since the beginning....the Zoomies do 6 months and who knows what the navy does out there at sea

But I believe their Sea Bees and Docs do 6 month tours.