For the national guard, how do I volunteer for deployments?

There are a couple of ways to volunteer for deployments. Probably the two best places to check for you are Guard Knowledge Online (GKO)* and Tour of Duty* and see if there are any spots (CAC restricted access ... you DO have a CAC reader at home. If not, you should get one).

Being in the Army National Guard, you'll have to have your state release you first. Most of the time (and especially for lower enlisted Soldiers), it's a rubber stamp, but it's not a guarantee.

Additionally, if there are any ARNG units that are deploying they are usually cross-leveled at the state level before they are kicked up to NGB for fill from other units. So, if there are other TXARNG units heading out the door, you have a good chance of being able to snag a slot of they are short.

Let your leadership know you are throwing your name in the hat to volunteer for a deployment and have them pass your name up the chain to the state G1.
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* GKO - https://gkoportal.ng.mil/Pages/Home.aspx
* Tour of Duty - https://mobcop.aoc.army.pentagon.mil/ --- I believe they still have it limited to access from a .mil site, so you'll have to be at your unit to check (i.e., no access from home)

Also check out
Www.dfas.mil/Pfi

Check with your unit to contact MOB office for your State. Somewhere at JFHQ in every state is a CWO who knows what unit is NOS’d, who has one upcoming and who is in the pipeline as well as what units need backfill