US 'problem' as of today:

~2,500 US Marines + elements of the 82nd Airborne (several thousand, incl. ~1,500 surge) deployed to the Middle East; positioned regionally, not reported conducting ground combat inside Iran
https://www.reuters.com/world/us-deploys-marines-middle-east-2026-04-11/

Iran has: About 570k–650k active troops; ~350k reserves + Basij could raise mobilizable manpower to ~900k–1.2M. (IISS/Wikipedia estimates)

https://www.iiss.org/publications/the-military-balance