Note:  Naturally, after I've written and shared this out, someone finds a guide on this subject that somehow I did not in my own search for one.  Go figure.

Keeping with the recent focus on modern-day military equipment, I am inspired to turn my focus towards hand grenades (and by extension, all other thrown bombs).

I don't often see much discussion on these kinds of weapons.  I know people use them, but I haven't run into much discussion on them where I tread, and haven't really found an opportunity to use them in any games I've run.  Now that I am working with more modern, military style campaign building, I find myself actually looking at the rules and realizing that I didn't really fully understand them.

It's not that they're especially difficult to understand, but that there's a good number of rules that influence the outcome of a grenade attack, and unfortunately they're spread out over a few different sections throughout the GURPS Basic Set.  Here's my attempt at compiling them and presenting them with examples of use in a manner to make sure I understand it, as well as putting it together for others who are just coming to it as well.

Grenades in GURPS


Grenades are best deployed with the Throwing skill, as given on Basic p.226.  This is an Average, DX-based skill.  While there is a default for unskilled people (an unusual DX-3), you can sidestep it a bit when throwing something at an area (a hex), which just uses straight DX.  Knowing the Throwing skill at DX+1 or DX+2 adds one or two to your ST score, respectively, when calculating how far you can throw a grenade, which is very useful for would-be grenadiers.

We'll be dealing with fragmentation grenades in this article.  These have extra rules attached to them, given on B269, that deals with the explosive and shrapnel factor of it - i.e. very important to this grenade type.  These rules are further explained on B414 under Explosions and Fragmentation Damage.  Fragmentation is a Linked Effect, so stop by B381 when you have a chance.

B277 has the actual weapon statistic entries for grenades (of which there are a very good variety), which I've reproduced an example of below.

B355 expands on throwing things in general. This is where you'll find the rules for figuring out how far you can throw an object (dictated by the objects weight and your basic lift) as well as how much damage being physically struck by a thrown object can inflict.  There's also a small text box on how to handle catching and throwing objects back at your opponent, should you be so inclined to do so.

B410 has a Special Ranged Weapon entry for grenades. This talks about maneuvers for getting them ready in hand, pulling the pin, and how fuse delays come into play with aiming.  Here is where it is stated that the time to detonation begins as soon as the pin is pulled, which implies that the "generic grenade" either has no safety handle (spoon) or that your character typically never uses it.  This is corroborated by High Tech p. 190, though a provision can be made for not allowing the lever to move at all.

B413 adds a bit more to the pile, with Area-Effect Attacks.  This is most useful for fragmentation and incendiary grenades, since their damage doesn't reduce with range.

B414 has notes on attacking an area, in a text box up top.  This is where you will find the rules on handling scatter, and bonuses to attacking an area (that are somehow different from the ones given in the Throwing skill entry).

Don't forget B550 for the Speed/Range Table, either!

For defenders, you need not only be familiar with the basic Dodge active defense, but also Dodge and Drop and Dive for Cover as given on B377.

Random Hit Location and Large Area Injury on B400 are also likely to be referenced - the former comes into play with Fragments, and the latter with the grenade's concussive Blast effect.


That is a wide variety of pages for a single weapon.  This is why I feel the need to break it down and recompile it here.  Hopefully this can serve as a good reference document for other players.

Throwing Frag!


Our frag grenades will be thrown by one Cpl. Harris.  He's a fit lad at ST12 DX11, and well practiced in his grenade drill at Throwing 12 (former bowler, perhaps).

He will be throwing a generic TL6 Fragmentation Grenade as given by Basic Set, with the following stats:



The target is a small group of three enemy combatants behind a sandbag barrier.  He has figured that throwing a single grenade at this group, over the sandbags, would be far more efficient than trying to engage them individually with his rifle.

To pull this off, he'll need to:
  1. Figure how far he can throw his grenade, and if he can reach the enemy with it
  2. Throw it and figure out where it landed
  3. Determine the grenades blast radius and who gets caught in it
  4. Figure how much damage the grenade does to valid targets and inflict it
Let's get a handle on this by going through the process step by step.  Once you know it, it's really not that hard - coming in as a new player (or new user of these particular rules), though, can be a little confusing.

STEP 1:  FIGURING OUT THROWING RANGE

First, let's get throwing range out of the way.  Range for throwing an object is determined by the Distance Modifier, governed by the ratio between the weight of the object and your Basic Lift - the grenade, in this case.  B355 has the means of determining this.

All of the grenades in Basic weigh a pound.  Our soldier doing the throwing as a ST of 12, so his Basic Lift is 29 ((12*12)/5).  The ratio then is .034 (1/29).  The chart only goes as low as .05, which gives us a 3.5 Distance Modifier.  We then take our ST score and multiply it by the Distance Modifier, and that will give us our range in yards.  Ordinarily, that would be 42 yards (12*3.5).  Quite the toss.

BUT WAIT!  Or trooper has Throwing at DX+1!  This means that, while the weight ratio calculation is untouched, our effective ST for the purposes of throwing distance is actually 13 (B226)!  So, unlike an untrained but otherwise strengthy combatant, Cpl. Harris can throw his frag out to 45.5 yards (13*3.5). 

This distance is a consistent number for a given thrown object - good idea to note it on your character sheet.

Note that the U.S. Army's FM-3.23-30 (2000) mentions an "average" soldier can throw a 21oz MK2 grenade (a TL6 grenade) 30 meters (32.8 yards).  The later 21oz (sic) M26 "lemon" has an average throwing range of 40 meters (43.74 yards), and the modern 14oz M67 is between the two at 35 meters (38.27 yards).  So if you're not used to pitching for range, our trooper here isn't all that unusual.

STEP 2:  THROWING AND FIGURING OUT WHERE THE GRENADE LANDS

Once you figure out how far you can throw it, we figure out how well we can throw it somewhere.  This is done with your Throwing skill.  Cpl. Harris has Throwing 12.  Since this is a ranged weapon, the attack takes on range penalties if it's going any further than 2 yards.  The Speed/Range Table on B550 gives you the list of distances and their associated penalties.

The soldier also needs to make a decision:  Is he throwing it at a specific target, or in a general, fairly narrow area (i.e. the hex the target is standing in)?

If this is at a specific target - such as an enemy soldier - you deduct your range penalties and target location modifier from your skill and move on with the throw, using a 3d6 roll against Throwing to determine if it hit your specific target or not - we'll see more on that in a bit.

If the soldier is just throwing his grenade at a general area, he's in luck - there's a +4 bonus to skill for doing that (B414).  Given that these things go boom and have a considerable area of effect, this is usually the best bet.  There could be times when you want to smack an enemy directly with a grenade, though - consider the plasma grenades from Halo, or an impact detonation grenade against some kind of robot or vehicle.

Now, if our soldier tries to throw the grenade AT a specific person, the target gets an Active Defense roll - Dodge.  First we figure out if you hit them or not - success or failure against Throwing, plus or minus any bonuses or penalties.

If your Throwing roll is a success, the target gets a Dodge roll (assuming they're allowed an active defense) - just like you performed any other ranged attack.

If the target fails their Dodge, the grenade hits them directly (doing impact damage equal to the chart on B550 - thr-2 in this instance).  This is "best case scenario" for the thrower!  If there's a time delay fuse, the grenade will go off when the fuse runs out and we'll resolve what happens then.  If it's impact - boom.

If the target succeeds their Dodge roll, your grenade then scatters.  B414 has the diagram, but basically it'll go off in one direction a certain distance.  Direction is dictated by a 1d roll - each side of the target hex (starting at the direction you face/threw and moving clockwise) is chosen by the die roll.  How far it scatters in this case is by the target's Margin of Success on their Dodge, in yards, up to half the distance between the two of you.

This rule seems a little weird to me, since it implies that your target's Dodge causes the grenade to have a 1:2 chance of falling short - i.e. scattering back towards one of the three facings in your direction.  I'd say use common sense and cut those off and re-interpolate the results as a more logical direction.

If you fail your Throwing roll (non-critically), the target doesn't need to take a Dodge roll, and you go directly to "scatter" resolution.  Roll your 1d to determine direction of scatter.  Distance for scatter is in this case is your Throwing margin of failure - up to half the distance you threw the grenade.  Here, the scatter directions pointing back at you make much more sense (it fell short), so have at them.

NOTE:  If you're going GRIDLESS, invest in a "Scatter Die".  Some wargames use them to determine mortar and other inaccurate weapon scatter.

Now, instead of throwing it at an individual target, you can opt to lob the grenade at an area - a hex.  This automatically bestows a +4 bonus to your skill roll, again as mentioned on B414.  This skill bonus is pretty massive, as it takes our trooper up to effectively Throwing 16.  It makes it pretty clear this attack type is the superior choice when attacking a typical infantry target!

(Note:  The rules on WHY we get +4 in one section and +3 in another (Throwing skill entry) are not clear.  I'm leaning towards players without the skill getting +3 (flat DX) when they lob, and getting +4 (Skill+4) when they lob and have a point or more in the skill.  Don't take this as an absolute, though, and I haven't yet found an official answer to the question, either.  It's just one interpretation suggested to me by another.  If you find an official ruling, let me know!)

Anyone near the attacked area does not take a Dodge defense roll (since it wasn't thrown at them specifically).  Instead, they get to Dodge and Drop, as given on B377, after the grenade finally detonates.  We'll talk more about that shortly, as it's only done in response to the explosion itself.

(The target could also Catch and Throw the grenade back, as seen in the "Catching" text box on B355, but we'll leave that out for this article.)

STEP 3:  FIGURING OUT WHO GETS HIT

Moving on, once you've done your Throwing roll, resolved scatter, and determined defenses, we move on to the nasty bits of the attack - resolving the explosion.

Grenades usually have a fuse - given in the statistic line as a number of seconds.  Remember, unless you "cook off" the grenade, the count-down starts counting from the turn you throw, so the grenade might not go off right away (giving targets more time to react).

Once the grenade detonates, though, we have a couple steps to determine who's in danger and how badly they can be hurt.  I'd imagine if the grenade lays on the ground for a second or two before detonating, opponents in the area may use that opportunity to get away if they're still able to Move.

First thing's first - what's the blast radius of your grenade?  This can be calculated ahead of time, so note this on your character sheet if you like.  For a fragmentation grenade, we have two radii to concern ourselves with - the concussive blast radius, and the fragmentation radius.

Concussive blast radius on explosions of all types is twice (2x) the number of damage dice, in yards.  B414 has these rules.  Our TL6 Fragmentation Grenade does 4d of crushing blast damage.  That means this grenade's blast is dangerous out to 8 yards (2*4).


Range for the fragments is resolved in a similar way, but with the metric given under Fragmentation Damage on B414.  This is five times (5x) the number of fragmentation damage dice - again, resolving to yards.  A TL6 Frag has 2d of fragmentation damage, so the shards go out to 10 yards.

Everyone within 8 yards needs to worry about some kind of blast damage, and everyone within 10 yards needs to worry about some kind of fragmentation damage.  Double trouble for anyone who's inside both ranges!

Note:  GURPS is only concerning itself with casualty radii - real fragmentation grenades can physically send shrapnel at distances over 200 yards, depending on type.  Outside of the casualty range, however, they're not particularly dangerous to people.

When the grenade detonates, the opponents reacting to it get their Dodge and Drop defense from B377.  Note the Diving for Cover sub-rule.  This defense is pretty potent - users get an increased Dodge stat against the attack, and can potentially move one hex towards cover.  Unlike Dodge and Drop against bullets, Diving for Cover seems to allow cover to count against the explosion right away.  Probably because you can see, and react to, a grenade more easily than a bullet.

If the targets are lucky and pass the roll, they can move and change posture in accordance with the rules on B377.  This could move them a bit more away from the blast (or even completely out of range), reducing damage potential.  By changing posture (typically to Prone), they become harder to hit with fragments, in accord with Ranged Attack Modifiers.

This is one of those occasions where even a successful defense roll isn't a surefire way to avoid injury - the targets would need to get behind cover that can completely absorb the damage in question - simply passing the Dodge roll opens up the option of Diving or Changing Posture.


If the defenders fail their roll, however, they are in for a world of hurt - they simply weren't fast enough to get out of the way, and will take the blast where they stand, how they stand.

Note that it isn't super explicit who can take this roll.  In my GMing opinion, I'd say anyone who is able to react and within direct Line of Sight to the grenade should probably react in some way, unless they have some kind of computer or veterancy experience that lets them know if they're actually in danger or not.  This would make a grenade more effective than it seems at face value for forcing people to keep their heads down.  You or your GM may disagree with me on this.

STEP 4:  FIGURING OUT DAMAGE 

Ok, so we know how far our damage goes, we've figured out what objects on the hex are in these ranges and how well they're defended - that means it's time for everyone's favorite bit:  resolving damage against your opponent!

As mentioned before, someone caught in the blast potentially has two forms of damage coming at them - the crushing concussive blast wave, and the sharp cutting fragments.  Double trouble indeed.

First thing is first - you need to figure out how far your unfortunate enemies are from the center of the explosion, because blast damage decreases linearly with distance from the bang (not fragmentation damage, though!).  Count hexes (or your preferred distance figuring if gridless).

Once you've got distance from the blast figured out, go ahead and roll dice for the explosion damage.  A TL6 Frag will get you 4d cr ex at the blast center.

The concussion damage is a single hit per target - a given target just takes that crushing damage once, and that's that.  Where they take their damage (which dictates how DR will influence it) depends on if your game is using Hit Locations or not.  If you are using Hit Locations, the blast appears to be Large Area Injury as given on B400.  If you are not using Hit Locations, it counts as having hit the Torso only.  This isn't super clear to me, though.

Each target gets a separate roll, near as I can figure with RAW.  Other players I've spoken to seem to think this is the best bet, because explosions can at times be a little unpredictable.  If you disagree, you might want to simply roll once for the explosion and use the resulting dice to figure out damage for everyone in the radius.

Damage on the concussive blast is reduced from the center by 3x the distance from the actual hex the grenade went off in.  So if the target was 3 yards away, damage from the explosion are divided by 9.  Very quick falloff for damage, here - average rolls stop being damaging at 5 yards for concussion.  Top end damage gets you out to 8 yards concussion, and still deal (1 point of) damage.  For a TL6 Frag, anyways - later ones have more explosive force and subsequently wider radii.

Once you have it figured, apply DR to the remaining basic damage, and figure out Injury.

Note:  HT181 adds a new optional rule about explosions in confined spaces; this is a worthwhile read as it increases the crushing damage if the area in question is smaller than the explosion's radius and fits within a certain damage threshold.  It well represents reality.

Unlike a blast wave, fragments can bite a target more than once!  Once you figure your explosion damage, you actually need to figure out how many times someone within the frag radius is struck by shards.  This is much like firing a weapon more than once at the target in a single turn - the grenade has "Skill 15" for its own fragments, and effectively has Rcl 3:  for every set of 3 the grenade makes its "skill" check against a target, it hits the target another time.



(That is, rolling 15 gets you one fragment hit, rolling 12 gets you two fragment hits, rolling 9 gets you three...etc.)

Keep in mind that as a ranged attack, there are mods to the grenade's skill roll - Distance (B550), Target Posture (Ranged Attack Modifiers, B548), and the target's Size Modifier.

Taking fragments is automatic if you're standing on the frag when it goes off, but it's not clear just how many shards this results in.  Personally, I'd consider it the max - rolling a theoretical 0, perhaps - for 5 hits.  I think if you're standing on a grenade when it goes off, you should get wrecked.  This would corroborate with B415, which talks about someone laying on a grenade taking maximum possible damage.

Use the Random Hit Location table on B552 to figure out where the shards hit, if you're using Hit Locations.  If your target has gone prone, you may need to consider what parts of their body are actually accessible to the blast; I've seen real-world advice for soldiers mentioning pointing your head TOWARDS the grenade, since that's actually your best defended part - diving with your legs towards it may result in fatal injury to the arteries in your legs.
NERF or Nothin'!

Keep in mind Cover the target is behind - if you roll a Hit Location behind something, that object has its own level of DR it can provide.  This is how Dodge and Drop protects you - by making you harder to hit by being Prone, by potentially making you further away, and possibly puts you behind something that will absorb the damage of the attack in question.

If you don't use Hit Locations, the damage is directed against the Torso.

Once we know how many times your target is hit and where exactly they are hit, we determine how much damage each shard does.  Roll your dice for each shard (2d cut in the case of our TL6 example here), just like you would for an automatic weapon, and resolve it against that location's DR (applying cut modifiers for damage that makes it through).

Average basic damage rolls on those damage sources is 14 cr (explosion) and 7 cut (per fragment), respectively, without any mods taken into account - this kills the man.  This should be some motivation to wear your frag vest and helmet!

As a reminder fragments do not suffer a damage fall-off due to distance - they fly out and seem to do full damage right up to their radius limit - 10 yards for this type of TL6 grenade.  This is in line with realistic expectations, as it is typically the fragments that do most of the casualty production with these weapons - hence the name.

Wrap Up and Other Considerations

I think that is just about everything.  Some minor details remain - explosions count as incendiary so may ignite flammable things, for instance.  Generally, though, you should be set for all ordinary situations.  Figure your range, figure hit or miss (and where a miss ends up), figure who's in the blast range, who is hit where, figure basic damage, figure how range and DR reduces damage, and then inflict the damage.  It follows a logical process without any major disconnects with reality.  It's just a lot of page flipping if you're learning this for the first time, and a couple rules gave me a double take.

Keep in mind that because throwing a grenade is a ranged attack, so you can do attack maneuvers or call in other things that effect other ranged attacks.  I'd imagine you could AIM for two or so seconds (probably only after you have pulled the pin) to gain +1 to skill (Acc 0 only gets +1 on the second turn).  All out Attack:  Determined for an additional +1. Since GURPS doesn't consider the user to hold onto the safety lever by default, this time spent on Aim also runs the fuse down, reducing the ability for your enemy to throw it back at you.

Grenades can often be thrown Blind (B389), or as a Pop-Up Attack (B390).  Very useful, and in line with the Army's teaching.  While not explicitly mentioned in Basic or High Tech, a cooked-off grenade can also be thrown such as to explode in the air above the target.  I'd imagine this is best against sub-surface defenses that you're not confident in being able to accurately land a grenade into.  B415 has rules for air-burst explosions.

As you can see, grenades can be a very potent tool.  It's possible that someone with little in the way of training or skill can use them pretty effectively.  A substantial portion of even "missed" attacks still have the potential to deal damage, unlike a firearm.

Even a regular ST10 DX10 individual with no points in Throwing who Determined to throw a frag at an Area (net DX+1), with a second to Aim (net DX+2) is fairly effective on their own.  Sure, no bonus to ST for range, but that's still a fair distance (35 yards), AND they can potentially wound or kill multiple opponents.  Range penalties are still a problem, though, and there may be a question of Familiarity penalties.



Closing

Grenades are very useful.  While they're firecrackers compared to 81mm mortar shells or 155mm howitzer rounds, they still give infantry forces a viable tactical option to respond to a variety of battlefield threats, often while exposing themselves to minimal risk.  As you can see with the numbers, even average rolls can remove someone from combat completely if they are close by the explosion.

There are a variety of other grenade types, and GURPS handles them all.  I may at some point talk about the unique ways that they deliver their payload, such as smoke or incendiary.  Or even Infrared Signalling.  A bulk of all this content here will still apply, so it's just the specifics on their warhead.  I had intended to add diagrams based out of Roll 20 but getting them looking good wasn't something I felt I had much time / patience for at this point.

Thanks for reading!

Cheers!