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I'm working on a story that has a mix of futuristic tech and D&D style magic, so I was wondering about this interaction.

(Note: I'm "houseruling" that Magic Missile can be used to attack objects)

Even a really pokey airplane flying at 136 miles per hour crosses Magic Missile's 120-foot range in under a second, as the craft is flying at just under 200 feet per second. That's peanuts compared to something flying supersonic or hypersonic speeds.

Something going Mach 2 crosses 2,251 feet in one second, and something flying at Mach 16.7 covers 18,793 feet in that same second.

So, would it turn a normally 'always accurate' attack into a 'roll to hit' attack, or would it even be possible to hit such fast-moving targets with a spell like Magic Missile directly, or would you have to use spells that simulate flak instead?

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  • \$\begingroup\$ This is clearly opinion based and since it's the OP's story only their opinion matters. \$\endgroup\$
    – Dale M
    Sep 7 '20 at 5:45
  • \$\begingroup\$ @DaleM, I'm trying to get the opinions of others to help my story 'work' better with mechanics. I read causally about D&D, but I don't know that much on the details. Just because I could arbitrarily say something 'works' doesn't mean that it makes sense, ergo I am trying to ask people who know better. \$\endgroup\$
    – Jazzyamx
    Sep 7 '20 at 8:14
  • \$\begingroup\$ you need to ask on a forum - this is a Q&A site \$\endgroup\$
    – Dale M
    Sep 7 '20 at 21:05
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There isn't any ruling that specifically applies to your situation. Generally, when using a spell like magic missile (and attacking in general) the creature that you're attacking is not in motion. You either attack on your turn, where enemies are stationary, or as a reaction (such as an opportunity attack), and the attack is resolved in the moment that reaction is made (unless another creature reacts to the reaction, then the secondary reaction is resolved first). In addition to this, projectiles like arrows or magic missile bolts mechanically travel to their target instantly – there is no consideration of travel time, and as such there is no consideration of projectile speed.

RAW, with the only modification being that magic missile can target the vehicle, then as long as the target is in range when the magic missile spell is cast, it hits as normal. The player can ready the spell to fire when the plane enters their range and everything goes off without a hitch.

As the DM, though, it's perfectly reasonable for you to rule that because of the high speed, players roll with disadvantage on ranged attacks when targeting exceptionally fast-moving objects. Some might even say that's it would be unreasonable not to, but that's a matter of opinion.

You also might want to house-rule magic missile's range up a bit, so that the planes don't have to fly below 120ft to get hit by anything other than a Warlock with the Eldritch Spear invocation.

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