I am currently working on an idea where a team of elite SWAT members (the group) is at the right time at a wrong place. It is a hostage situation, but something about the whole situation is deeply wrong; the purported "terrorist attack" does not fit, the opponents are much more trained and experienced, other SWAT teams are "incidentally" placed out of reach. It soon becomes clear that the attackers expected that they have enough time for their mission and are experienced enough to hold the police off. The group get the idea that their leader must have got a tip and moved a purported "training mission" unexpectedly on last notice to the area.
So what I need is a system:
- Fast paced during action, but allows longer planning.
- Supports automatic weapons, grenades, stun grenades, tasers whatever
- Force multipliers for surprise, coordinated action, stunning, scouting etc. The system must be able to put the team into such an advantage that the risk of dying or traumatic injury with a lethal combat system could be negated with players who know what they are doing.
- Should allow to handle close combat including knives and improvised weapons.
I will take the place of experienced opponents. I will inform the players about the room structure, the position of hostages and combatants etc., but leave the planning to them. The players can position themselves invisibly, but if they screw up, they must inform me ("Guard A hears metal scraping 10 meters in the northwest").
Immersion should be the most important aspect. That means the exact probability function is not important, but dice evaluation should be fast. I am not bound by a specific image (Hollywood, realistic gunfight), but the system should be lethal and therefore a punishment for any hothead and low risk for a carefully planned and executed attack.
Time granularity: Definitely not setup finished roll fail/success. Player should be able to modify their behavior inside combat, so I think we have a moderate, adjustable frame for preparation and a short one (0.2-1 seconds) per action in combat. That may sound small, but I cannot think of an extended firefight which is not lethal.
Gun details: I would like have a "standard" equipment (pistol, revolver, RPG, grenade) which is not overwhelming for a new player, nothing more. But if someone is really into it, the system could readily allow to modify and fine-tune his weapons.