Turns consist of either route moves, search moves, or combat melee rounds (melee turns). Route movement is used when the players wish to cover great distances rapidly. Search movement is used when the players are conducting a careful investigation of an area. Combat melee turns are generally used when players encounter hostile beings.In those few sentences, we see can discern the primary activities of Gamma World characters: wilderness travel, exploration of ruins, and combat -- just as in OD&D.
Route movement is on a scale of 1 to 10 kilometers every four hours, depending on the type of terrain over which the characters are traveling. It's noted that, while this may seem unusually slow, route movement assumes the character are, in addition to walking, keeping an eye out for sites of interest, such as ruins of the Ancients, thereby preventing their moving more quickly. Search movement is on a scale of 1 meter every 10 seconds. Again, this assumes a slow, more methodical pace than is typical, since the goal is to look for evidence of anything interesting, including traps and dangerous devices. Melee rounds are 10 seconds long, which is identical to the length of a round in Metamorphosis Alpha but at variance with OD&D.
Combat begins with a determination of surprise, as in OD&D, by rolling 1D6, with a roll of 1 or 2 indicating surprise. Initiative is subsequently determined by a 1D6 roll, modified by high Dexterity. There are a couple of interesting wrinkles here. Throughout the text, it's noted that the winners of initiative in a round has the option of "first strike," which would imply that they can decide whether to attack first in a round or not. However, the text only indicates that "the side with the first strike option may exercise the option and attack, or take this opportunity to retreat, negotiate, or whatever seems feasible at the time." Furthermore, it's noted that only initiative ties indicate simultaneous action, but there's a "dying stroke" rule that calls this into question. The rule states that
In some rare instances (such as the use of an extremely powerful weapon or mental force) combat will last only one-half of a melee round - that is, simply one attack and its results. For example, a Mark V blaster can conceivably hit a target for 30 points of damage. A creature that can withstand only eight points of damage before death would be disintegrated by a 30 point hit. On the other hand, it the blaster did only 10 points of damage when it hit, the creature would still die, but it would also be allowed a “dying stroke” (remember this is simultaneous) and would complete the melee round with its final counterstroke before it dies. It is up to the referee to determine if a dying stroke is allowed, but a good rule of thumb is: if the hit that killed the target did so with an “overkill” of less than half the hit points the target had left, a dying attack is allowed if the combatants are at close range.Now, it may simply be that the dying stroke rule is a very particular rule, applying only in cases of initiative ties, but it's hard to say, since the text isn't explicit on this point. Regardless, it was a rule I never used back in the day, even though I was aware of it.
There are three types of combat in Gamma World, each of which is governed by slightly different rules. These types are physical combat (which includes ranged weapons), mental combat, and creature combat. Physical combat is the most general, consisting of an attack roll and, if successful, a damage roll. Unlike D&D, Gamma World characters' combat effectiveness isn't necessarily tied to experience. Instead, it's based on the "weapon class" of the weapon used in physical combat. Weapon classes range from 1 to 16, with primitive weapons being at the low end and advanced ones at the high end. The weapon class is cross-referenced on a table against a target's armor class, which ranges from 10 (the worst) to 1 (the best). Weapon classes are an interesting idea, since they take into account weapon vs. AC modifiers but without the need for an extra calculation. Thus, there's not a straightforward progression in terms of effectiveness from class 1 to class 16 against any given AC, with some lower class weapons being better than higher class ones against a given AC. Likewise, the "to hit" number progressions follow no regular pattern even within a single weapon class, meaning that the use of the chart is absolutely essential.
Mental combat operates similarly to physical combat in broad outline, but, instead of comparing a weapon class against an armor class, one compares Mental Strength against Mental Strength. A chart then provides the "to hit" number needed to succeed, with damage being determined by the mutation used. Mental combat requires sufficient concentration that a character cannot attack mentally and physically at the same time. Five successful mental attacks (or mental defenses) increases a character's Mental Strength by 1 point. It's not specified if this is five successes in a row, but that's how we used to play it, since it's much too easy to increase a character's ability score otherwise. Creature combat does not use weapon classes but rather hit dice against armor class, as in D&D. Of course, this only applies to unarmed attacks. Creatures that use weapons use the standard physical attack chart.
There are only two ranges for all weapons. Up to the maximum range listed, a weapon suffers no penalties or bonuses, regardless of whether it's fired at 10 meters or 100. At any range up to twice its maximum range, there's an across the board penalty of -5. Primitive weapons have two damage values, one for man-sized and smaller creatures and one for large creatures. Gamma World also has simple fatigue rules for lengthy combat, which means any combat lasting more than 10 rounds. Certain primitive weapons and certain types of armor have penalties associated with them, applied either to the weapon class or the armor class when using the appropriate physical combat charts. Having a high Strength mitigates this somewhat. Of course, in my experience, it was rare for combats to last long enough for fatigue to become a factor, as Gamma World battles could be very deadly.
Morale is handled with a 1D10 roll, modified by Charisma. A roll of 3 or more on 1D10 is all that's required for intelligent creatures to keep up their morale, while a 5 or more is needed for unintelligent animals. Morale rolls, once used, are required every round thereafter until either combat ends or morale breaks. Of course, just when morale rolls are required is entirely up to the referee, as there is no definitive listing of when they're needed. This seems very typical of first edition Gamma World: simple rules that rely heavily on referee judgment to function.