What investment options are there for the military if any?

Indeed, the 2022 IRS elective deferral limits are $20,500, and Agency matching contributions don't count against that limit (if any, for those under the BRS retirement scheme).
TSP is low cost, high quality, user friendly.
Cheers, WKB

LtCol William Bentley - Yes sir, I can't imagine an E5 is maxing out the IRS limit through TSP alone.

Something like $783/pay period? If they had a large bonus (and many do these days), or just lived a quiet life of hermitage in the barracks, I think $1500/month COULD be done...but not very likely. Even less likely if with family. Perhaps if spouse worked, though. Honestly, not a likely scenario even for a company grade officer unless they were serious committed to saving for retirement and not many are at that age. My very first ever exposure to retirement savings investments, etc., was with a group of my peers, lieutenants all, who were discussing (back in the early '90's) how the interest rates were affecting their investments. I was intrigued; these guys had invested much of the money they made while deployed to Gulf War I, all the deployed pay, all the money they usually spent on wine and women and Lieutenant Mobiles ... they invested. I was fascinated! What a concept! Actually seek to save money? Find ways to improve returns on investment? Wow. And I thought I was a well-read, smart type of guy. But clearly my college education and formative experiences missed out on something. But you know the deal, even $25 or $50/month over time means bigger $$$ someday. Cheers,

CPT (Join to see) is absolutely correct - TSP is the absolute best option available for investing. In general, the best 'save for the future' way to go will be to invest with your employer sponsored savings program .. ESPECIALLY if they match contributions (which DoD does up to 4% of your base pay).

I would often tell my Soldiers that if they are just starting out, the general "hierarchy of investing" for them is the following:
1) Put in up to the matching your employer gives you for your retirement plan contributions (save for the future)
2) Pay off those credit cards (stop the bleeding) and other high interest debts
3) Maximize your retirement plan up to the IRS limits (save for the future)
4) After you do that, we can talk more (IRAs, etc)

Some situations may be different, but this is a good general approach - ESPECIALLY if you don't have a plan otherwise.

Those are problems, of course, but the program is a Vietnam War era relic. We're lucky it even still exists at all. Better something, than nothing.
TSP is a better option, frankly, as the time horizon of SDP ends with the deployment, whereas TSP has much better investment horizons...
CHeers, WKB

CPT (Join to see) - Accurate in general, but a few tweaks.

You're correct about the limitations on the salary, but a Soldier can deposit more than a month of pay if they have written approval from their Commanding Officer attesting to mission requirements and the lack of finance support.

Regarding "where", downrange is one of the categories. The other two are serving in a HDA (which could be considered downrange as well) and in a designated direct support area of a combat zone (which may or may not be downrange).

When I used it in RVN, I could deposit base pay and hostile fire pay. Only drew $13 overseas pay, which was plenty to live on. So now if you can only deposit base pay it still a good deal. I mean, how much money do you need in a combat zone, beer and smoke money, that about it. Army gives you everything else.

MAJ Ronnie Reams - You can deposit up to your entire paycheck - this includes all allowances. Apologies if I was unclear somewhere.

Agree about the "how much money" comment. I think during DS/DS, OIF and OEF I survived weeks without ever taking money out of my wallet.