With IPPS-A in place, what are the new steps for submitting for Retirement from the USAR?

IPPS-A.

Submit a PAR under the self-service. The 'Effective Date' will be your date of retirement and select "Admin Records Correction" for the 'Action'. An additional box will appear and select "Voluntary Retirement Request - Enlisted"

Make sure to include the supporting documents* (check to see if there are any that local policy requires as well) as attachments to the PAR.
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* Supporting Documents - https://www.usar.army.mil/Retirement/PayApplication/

I know this doesn’t pertain to your question, but is good information once you’re out and in the gray area.

For Army National Guard, Air National Guard, Army Reserve, Navy Reserve, Marine Corps Reserve and Air Force Reserve Gray Area Retirees, there is a new avenue to stay connected and informed between the time they stop drilling and the time they start receiving retired pay.

https://www.dfas.mil/RetiredMilitary/plan/Gray-Area-Retirees/fbclid/IwAR1XWjZBPbfi3hjyiAvOR5P73WagVhrSJs5MipbkXbaS_nPAPDDiyXQ3iA8/

Master Sergeant, I have two words for you... "Shared Physical" and stay on top of the VA during this process.