Army Vehicles in Saints Row 2 (Xbox 360)? Not in Base Game
No military/army vehicles are obtainable in Saints Row 2 on Xbox 360.
Why
No DLC Adds Them: The three DLC packs (Ultor Exposed, Corporate Warfare, Ultor Assault) add corporate security vehicles, not military.
Console Modding Impossible: Unlike PC, Xbox 360 does not support custom vehicle mods.
In‑Game Spawns: The closest are FBI (black SUV), SWAT (armored truck), and Police variants. No tanks, APCs, or jets.
Military Vehicles in Later Saints Row
Saints Row: The Third: VTOL (F‑69), Tank (Crusader), Cyber Bikes (DLC).
Saints Row IV: Mech Suit, UFO, Tank, all customizable.
Saints Row (2022 Reboot): VTOL, Tank, Hovercraft via progression.
If you want military hardware in Stilwater, you're limited to the Tornado (attack helicopter) (cheat: #2666# on phone) or the Vulture (heli)—neither are ground army vehicles.