Clear the Ace bonus objective for the final mission (Mission 4.5 - Final Count Down) to unlock the fourth set of weapons for the SR-71 Blackbird.

This weapon pack includes the game's "super weapon", the A-SLAMR. The A-SLAMR does not recharge during a mission so once you fire it, you used it (for that mission).

BOOOOOOOOOOOOOOOOOOOOOOOOOOOOM!