Time of Flight in pen-and-paper RPGs

This is a response to a post +Gerardo Tasistro made a bit ago about when time of flight matters in RPGs. He’s positing that it’s not enough to know when in a turn sequence you act, but sometimes it’s key to know when – sometime later – the consequences of your action actually occur.

I started to reply to him, but my post started to get long. Not just because I had stuff to say, but there is actually a lot to unpack in some of his assumptions, and I’m not talking about physics.
So, let’s take this in two parts. The first part addresses his asssertion that time of flight will be a significant player in many/most modern firearms encounters.
We’ll start by excerpting his final paragraph – but the real interplay that led to this post was in the comments, so it might be worthwhile to check those out.

Flight time matters a lot more in modern combat RPGs due to the nature of the weapons themselves and there much longer ranges when compared to medieval ranged weapons. Yet some of the issues apply to fantasy settings as well. How do you take flight time into consideration when running your game?

Time of Flight – when it matters


While the machine-gun chart supports his point (50% of targets engaged at ranges more than 750m, the other chart (reproduced below) contradicts it a bit. 80% of all fights, regardless of terrain, occur at ranges less than 300m, which is going to be roughly 0.4 seconds flight time for a bullet from an M16, and about 1.2s for a 9mm from a pistol.
The Defense and Freedom link is interesting, but even his conclusion says don’t give infantry weapons that can reach past about a half-second away, or about 300-400 yards. That’s well within the range that unless you’re looking right at the guy shooting at you, you effectively have no chance of perceiving and reacting to an attack. Most of the time, even that won’t matter. Boom, dead. Next time, learn to use cover, concealment, and movement.

Now, my game of choice is obviously GURPS, which resolves actions in interleaved one-second blocks. Not “A goes, that’s one second, B goes, that’s two seconds, etc.” but A goes, and then B through G have their turns somewhere in the time span between when A went and he goes the next time. It’s purposefully kept a bit vague, and there are LOTS of situations where on a second-by-second basis, a GURPS combat mightn’t make instantaneous sense. You have to get to A’s next turn, and then rationalize what happened.

For example, you can do pretty much infinite dodging, and so if you do a Judo Parry, and dodge three others, and there’s a retreat in there, and an attack where you grab someone, but . . . you really can’t narrate it completely until it’s over. You can try, but you won’t like it much all the time.

Anyway, on this scale, the Defense and Freedom link suggests that four times in five, the worst that would happen (at 300m with a pistol) would be A fires, a bunch of other people go, and then right about when A is about to take his next turn, the guy who he’s shooting at gets hit.
How would GURPS handle this? Well, at very long ranges, +Hans-Christian Vortisch wrote the “Time of Flight” rule into Tactical Shooting (p. 32) which gives an average flight time for rifles and pistols, as well as adjusts the hit percentages a random amount (you can walk into the bullet’s path, but mostly you are harder to hit).
But by and large, you shoot, you roll the results, and that’s it.
Now, that goes right out the window for bows, especially in ye olden days. A battlefield engagement with medieval warbows would happen as if they were the equivalent of artillery an machinegun fire: massed volleys at packed bodies of troope. And at 200-250m range – where the English expected their archers to be able to reach – a volley might take four or five seconds to reach that target.  The velocity of these bows is on the order of 40-50m/s, and that velocity is retained for nearly all of the flight. Modern bows are faster. High draw, high efficiency, and lightweight carbon fiber or aluminum arrows can hit about 90-100m/s . . . still two or three seconds flight time.
Hell, in the five seconds it takes for an arrow to reach a target 200m away, many GURPS combats are already over.
So I actually find Gerardo’s argument persuasive . . . but for ancient weapons, not modern ones!
He suggests, and seems to be designing a game around, breaking a typical 10-second turn into 250 millisecond increments. I don’t think he’s necessarily saying that you take 40 actions in that time. Rather, you take one, but the propagation of those effects is resolved in fairly precisely defined time scales.

Realism and Fun

While I find his pursuit of accuracy and detail interesting (and if you read this blog, you’ll see some of our tendencies are rather aligned), I hope he realizes that there are probably like five people on the planet who would put up with a pen-and-paper game that resolved actions in quarter-second increments. GURPS gets roundly criticized for its one-second time scale, and that IS a length of time where you actually get aphysical behavior from some weapons.

I think, also, that this search for realism hits right into what +Sean Punch was hitting on when we discussed the importance of realism in the gaming industry. (link goes to the YouTube video).

Ultimately, there are probably only a few situations where it really, really matters more when that bullet or burst hits than what your players will do to you when you make them track actions on that scale. There are already long, painful GURPS Forum threads about how weird it seems to have to take two separate turns to pick up a dropped weapon. The actions are discrete, but only make sense when viewed as a two-second holistic move. Wackiness ensues. 
There was an interesting thread about making GURPS turns 3 seconds long. While it didn’t really go anywhere (the one-second resolution is pretty ingrained into the system), there’s a point here. If you look at Pathfinder turns, each is 6 seconds long; older editions were even longer. GURPS are one second long. 
Now take a 5 minute grappling match. That’s 300 painful, second-by-second turns in GURPS. It’s a barely-more-tolerable 50 turns in Pathfinder. Old-school D&D, if I recall correctly, would be either 5-10 turns of 30s to maybe a minute. Ironically, the most gameable and palatable scale of this, where your players aren’t contemplating murder, are those that will sweep most of the cut, thrust, parry, reversal, close-shave moments under the rug. 
Hell, I wrote an entire article just to slow down the frantic-seeming pace of GURPS combat brought about, in part, by the one-second time scale.
Parting Shot
I started rambling a bit, so I’ll cut this off. I think that the notion of “there are some ranged combat effects that really need a delay between declaring the action and resolving it” is, by and large, a fine thing, I think that tracking it too precisely will probably lead to a game that’s totally realistic and totally unplayable. There’s too much that gets usefully subsumed into skill and die rolls, and breaking this down into detailed component parts is probably headed the wrong direction. 
That being said, if your game is based on 10 second rounds (to use his example from his post) instead of 1 second, well, an awful lot might happen in the first five seconds, so instantaneous resolution – especially based on I go, you go initiative, probably has a lot of artifacts to sweep under the rug. I understand why he’s pursuing it, even if ultimately I can also see why the additional complexity will significantly limit any future market appeal of such a system. Heck, one of my very first posts on this blog was about this topic!
Of course, market appeal?  Mass-market, that is. If you and three to ten of your closest friends are totally into it, well,  awesome.
And just by way of example, one of my old campaigns, a Black Ops campaign, had a moment of incredibly high drama based entirely on weapon time of flight and +Alina Cole‘s character being totally awesome with a rifle.
They were being engaged by a bad guy from something like a 1,000m distance. Maybe more. I think it was a mile or so. The bad guy had a 0.50 BMG, with a muzzle velocity on the order of 750-800m/s. I recall time of flight was something like two or three seconds.
My wife’s character had a recently acquired bit of alien technology – a gauss rifle with a muzzle velocity of something like 1,500 or 3,000m/s.
She was able to see the guy point and shoot at her, aim, fire, kill the guy, and then take cover from the incoming steel rain . . . all because time of flight mattered.
It was awesome, and could never have happened without taking time of flight into consideration. 
So I really do get where he’s coming from.
I hope I haven’t mischaracterized his thoughts and opinions in any way. If I’ve misstated his thoughts and intentions (and he corrects or clarifies in the comments), I’ll edit.

5 thoughts on “Time of Flight in pen-and-paper RPGs

  1. Ever encountered the timing in Rolemaster (at least the most recent public Beta of the game), Doug? Ten second turns, if I recall correctly, and you budgeted how you used your time. Figure out what percentage of that time you need to ready a weapon, or cast a spell, or make an attack, and budget for it, either with a "it must all fit in the turn, or it can't happen" rule by default, or a "fractional results carry over to the next turn" variant that really made a good deal of sense.

    It's a nice half-way point between "every turn a second" in GURPS and "some things you want to do take more than one second, so there's major actions, minor actions and free actions" from the d20 world.

  2. I've played in home brewed systems which ran on 1/100th of a second intervals, with different actions taking less time than others allowing characters to flow in combat a bit more realistically. All in all, it wasn't worth the extra bookkeeping, and if anything it made the combats take even longer for any given engagement.

  3. Phoenix Command used quarter second steps in a 2 second turn, and was pretty anal about time of flight too. Man I miss Phoenix Command… though it translates into GURPS very well, natch.

  4. I enjoyed the article.

    When designing BESM 2nd Edition, I deliberately picked "3-4 seconds" as an increment partly for time of flight considerations (as the game had a lot of long-range mecha combat) but also partly because 3.6 second in a turn allowed 1 KPH to translate into one 1 meter per turn, thus saving me the hassle of having a separate stat for speed.

    One trouble with very small increments is you actually hit a point where people's death/injury reactions are a bit too slow to resolve a fight

    One advantage of a longer time scale on the 5-15 sec range is that matches the "hit in vital area but not central nervous system, fall down" speed and also would realistically allow bleeding in 1 turn to 1 FP to or 1 HP increments, and also permit combat lifesaving where "I run up and stop the bleeding" feels more plausible and doesn't take you away from the action for 10 or so turns.

    Half-second or so turns might be fun for a game focused on robot and transhuman characters, to give the game some extra posthuman flavor. A small turn increment does simplify autofire a bit, and also means you could logically have modern weapons with one turn = 1 shot or burst of no more than 3-4 shots. Good for indoor fighting.

    GURPS does use time of flight for guided missiles, of course.

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