Combat Effects (OSS)

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Surface dwellers add 4 to their initiative rolls and suffer a -4 penalty to their attack rolls when fighting underwater. In addition, the swirling currents and dim visibility of a watery environment prevent characters from receiving any offensive bonuses from weapon specialization-including attack bonuses, damage bonuses, and extra attacks each round.
Certain magical items (such as a ring of free action), spells, and specially designed underwater weapons negate these penalties. These items are, however, quite rare. Most surface-dwelling adventurers who find themselves traversing murky depths do so at a distinct disadvantage.
==Melee Attacks==
The greatest challenge to any underwater combat is the resistance of water. Although weapons retain their mass and density underwater, water resistance significantly weakens their impact. As a result, only weapons that use a thrusting motion are effective underwater. For a complete listing of weapons that function underwater, check Table 44: Underwater Characteristics for Weapons.
==Missile Attacks==
Thrown weapons such as daggers and darts do not function underwater. In addition, normal bows and crossbows are not effective when used underwater, as their wooden components tend to warp and, in the case of crossbows, their firing mechanisms tend to rust and lock.
===Underwater Combat Proficiency===
Adventurers traveling through strange undersea environments need not go without defenses. Characters can become proficient in underwater combat and master practical fighting styles that prove effective in a marine environment. Through extensive training, proficient PCs learn to compensate for the inexorable pull of underwater currents and the resistance of water to the motion of weapons.
Characters with the Underwater Combat proficiency only add 2 to their initiative rolls and suffer only a -2 penalty to their attack rolls. The proficiency costs two proficiency slots and is available under the Rogue and Warrior proficiency groups. Its relevant ability is Dexterity. Adventurers who fill four proficiency slots with Underwater Combat may add their combat bonuses (attack, damage, and extra attacks) for a single level of weapon specialization (assuming the character is already specialized). However, under no circumstances can characters add the effects of double specialization or weapons mastery to their attack and damage rolls.
For those players using PLAYERS OPTION®: Skills & Powers characters, Underwater Combat costs four character points (or eight points to allow the use of one level of weapon specialization underwater). In addition, its relevant subabilities are Muscle and Balance. It has no initial rating.
==Optional Rule: Gradual Crossbow Decomposition==
Although not designed for use underwater, crossbows can function for a limited time when submerged. These weapons must make an item saving throw (as metal) against acid for every turn they remain underwater. Each turn after the first, however, the crossbow suffers a cumulative -1 penalty to its saving throw. Failure indicates that the weapon ceases to function.
In any event, the range and effectiveness of surface crossbows used underwater are extremely limited. Ranges for these weapons are reduced to one tenth of the original values. In addition, surface quarrels subtract 1 from their damage when fired underwater. Thus, the maximum range for a surface hand crossbow fired underwater is only 6 (60+10) yards or 18 feet.
Special underwater missile weapons do exist. However, such weapons are exclusively the purview of intelligent sea-dwelling societies-such as sea elves and tritons. Due to their somewhat different construction, these weapons require their own specific weapon proficiencies.
Such weapon proficiencies, however, are very difficult to come by and may only be appropriate for certain classes or kits (such as the buccaneer, pirate, and swashbuckler), or any character with a primarily nautical background. Earning a proficiency with a weapon designed for underwater use requires many hours of practice submerged in a watery environment, as well as a weapon crafted by an intelligent marine race. For the most part, such practice can only come about through magical means, and PCs will be hard pressed to find a teacher with the resources and inclination to impart his knowledge. After all, intelligent sea-dwelling races are reluctant to surrender their tactical advantage by giving a surface dweller an effective underwater weapon.
However, surface weapons are related to their underwater counterparts. Thus, a warrior proficient with a normal hand crossbow would receive a related weapon bonus, thereby suffering a nonproficiency penalty of only -1 (half the normal nonproficiency penalty, rounded up) when wielding an underwater hand crossbow.
DMs should note that all penalties incurred for nonproficient weapon use and missile range attack roll modifiers are in addition to the general underwater attack penalty of -4.
For example, Mara, a 4th-level fighter, has fallen overboard during a fierce storm. While submerged, Mara notices a shark about eight feet away. In an attempt to drive the predator away, she fires her surface hand crossbow. Since she is underwater, the fighter suffers a base -4 penalty to her attack roll. Unfortunately for Mara, the shark is at medium range for her surface crossbow and so she receives an additional -2 penalty. Mara, then, must make this shot with a final attack roll penalty of-6. Let's hope she's a good shot.
==Jousting==
Many marine races harness the abilities of surrounding sea creatures to aid their societies. For example, whales and other large aquatic mammals often help sea elves and mermen move heavy materials or obstructions, and sahuagin use sharks to guard their cities and dispose of waste.
Likewise, many underwater cultures utilize marine creatures such as dolphins, whales, seahorses, and so on-as mounts. In some cases, these mounts serve in much the same way as surface-dwelling cavalry horses.
When two or more mounted creatures face each other in underwater combat, they may "charge" directly at each other and engage in a joust. Jousting creatures do not need to roll initiative, as both attacks occur simultaneously. Characters with multiple attacks cannot attack twice in the same round during a joust. Rather, the characters may use their additional attacks to parry (see Chapter 9 of the DUNGEON MASTER® Guide for more details on parrying) the incoming lance attack; however, they must be equipped with some type of shield to do so.
Since lances are specifically designed to dismount riders, any time a lance inflicts more than 8 points of damage (after doubling the damage for a charge attack), there is a chance that the victim is knocked off his mount. Such victims must make a successful Underwater Riding Proficiency check (see page 81) or fall off their mounts. Unencumbered dismounted characters float up at a rate of 10 feet per round. Encumbered dismounted characters sink at a rate of 10 feet per round (40 feet if they wear metal armor or possess more than 30 pounds of equipment).
Occasionally, the force of an attack may shatter a lance. Whenever a lance inflicts more than 12 points of damage (after doubling the damage for a chargeattack) or is successfully parried with a shield, the lance must roll an item saving throw vs. Crushing Blow. (Treat the lance as Wood, Thin.)
Characters must have the Underwater Riding proficiency (detailed below) and a trained mount before engaging in an underwater joust. In addition, the normal 4 attack penalty still applies to submerged characters without such magical augmentation as a ring of free action.
===Underwater Riding Proficiency===
With this proficiency, characters can use underwater creatures as mounts. Proficient characters can easily direct such creatures and can even fight while riding their mounts-though they do not receive the +1 attack bonus for mounted combat. In addition, mounted characters with this proficiency can engage in underwater jousts. DMs should note, however, that non- proficient characters cannot ride underwater mounts.
Typical mounts include dolphins, small whales, seahorses, and sharks, though many other marine creatures can easily serve as underwater mounts. This proficiency does not, however, allow characters to train such creatures as mounts nor tame otherwise hostile creatures. A creature's training must occur prior to its use as a mount.
Underwater riding costs two proficiency slots and is available under the General proficiency group. Its relevant ability is Dexterity, and its check modifier is -2. DMs may wish to limit this proficiency to those characters whose backgrounds support such an unusual ability. Thus, heroes from a landlocked mountain community should not have access to this proficiency.
For those players using PLAYER'S OPTION®: Skills & Powers, Underwater Riding costs four character points. Its relevant subability is balance, and its initial rating is 7.