Grand Theft Auto III/Marked Man

Brief
Ray's been marked for assassination by the CIA for his recent animosity towards the Cartel, and he needs Claude to drive him to the Francis International Airport in Shoreside Vale within three minutes before they can get to him, promising he'll be rewarded for his efforts. The authorities are heavily guarding the lift bridge to Shoreside Vale, so you'll need to take the underground Porter Tunnel there.

Walkthrough
Despite the game's warning as you regain control, it is possible (albeit very inadvisable) to take the bridge. Your best bet is to hustle until you see the government agents in view, then hop out of the car momentarily to take them out with a sniper rifle or other strong weapon. They are heavily armed and are wearing armor, so expect strong resistance.

Otherwise, the underground tunnel is more manageable. Three minutes is plenty of time to get to the airport gate, at which point Ray gives you the keys to his emergency lockup and rushes inside. Head there and enjoy the cash, weapons (a sniper rifle, M-16, rocket launcher and flamethrower), and rare he left you as he sends best wishes from Miami. Be sure to get everything you can, as you won't be able to open the lockup again after this mission.