GURPS Underwater Weapons (TL 7)

Version 1.51

Underwater weapons are used by combat divers, a.k.a. frogmen, like the U.S. Navy SEALS, the members of the British SAS boat troop, the German Kampfschwimmer der Bundesmarine, or the Russian naval Spetsnaz.

The rules given in the GURPS Compendium II on p. CII61 for "Missile Fire Underwater" do not apply to these weapons, but cover normal guns, firing normal bullets. The weapons described below are especially designed to fire underwater and they use different ammunition with dart or bolts, not bullets.

Note also that the speargun in GURPS High-Tech (p. HT100) is an example of a commercial version for sport or underwater hunting. The military versions below are slightly more powerful.

If you read the rules on "Combat in and under water" (p. B91) you will more fully appreciate the usefulness of underwater weapons other than conventional hand weapons (e.g. knifes).

Some weapon descriptions have codes (e.g. [h, l, n, s, f]) indicating possible modifications/accessories. A code in round brackets (e.g. (s)) indicates that the weapon is already fitted with that extra. Click on the codes to go to the modifications/accessories page. Clicking on the weapon names brings you additional immages.

Underwater Weapon Tables (TL7)

Weapon Malf Type Damage SS Acc 1/2D Max Wt. RoF Shots ST Rcl Cost LC Holdout
Speargun Crit. Spcl 2d+2 12 4 150 190 5 1/4 1 10 -1 $2,000 5 -4
6×400mm (Hollow Steel Bolt) [l, f]
Note: This is a custom designed pneumatic speargun. The first examples of this weapon type appeared during WWII. It is using a compressed air reservoir (1 lb., $5) that is good for 12 shots and can be changed in 10 seconds. Air reservoirs can be charged from a standard diving cylinder. The gun fires two types of "spears" (technically rather bolts or darts), either a short one with a blunt broad round nose (range -80%) doing non-penetrating crushing damage (do not treat as bullet damage but as crushing damage like a punch; use p. CII53), or a longer pointed bolt, doing impaling damage. It is silent: -6 to hear shoots, -10 to recognize if unfamiliar with. Fired underwater 1/2D range depends on depth: at 5m depth 15m, at 20m depth 10m, at 40m depth 5m. Max is 1/2D ×1.5; SS is 14. The weapon can be broken down into three smaller parts, for a Holdout modifier of -2. Reassembling and loading takes 10 seconds. A set of 4 bolts of either type together with a fresh reservoir in a tough lightweight container weighs 3 lbs. and costs $100. For poisoned arrows look under Crossbows, on page 13 below. Use the Guns [Crossbow] skill.

 
Weapon Malf Type Damage SS Acc 1/2D Max Wt. RoF Shots ST Rcl Cost LC Holdout
Airgun pistol Crit. Imp. 1d+1 11 2 100 125 2 1/4 1 10 -1 $600 5 -3
6×270mm (Hollow Steel Bolt)
Note: This is the pistol version of the pneumatic speargun. It is using a compressed air reservoir (1 lb., $5) that is good for 20 shots and can be changed in 10 seconds. Air reservoirs can be charged from a standard diving cylinder. It is silent: -6 to hear shoots, -10 to recognize if unfamiliar with. Fired underwater 1/2D range depends on depth: at 5m depth 10m, at 20m depth 6m, at 40m depth 2m. Max is 1/2D ×1.5; SS is 13. A set of 4 bolts together with a fresh reservoir in a tough lightweight container weighs 2.5 lbs. and costs $100. For poisoned arrows look under Crossbows, on page 13 below. Use the Guns [Crossbow] skill.

 
Weapon Malf Type Damage SS Acc 1/2D Max Wt. RoF Shots ST Rcl Cost LC Holdout
IPME APS Crit. Imp. 2d+2 12 4 88 132 7.5 10* 26+1 9 -1 $750 1 -4
5.66×120mm Model MPS (Steel Dart) [l, f]
The Russian APS underwater assault rifle fires a 120mm long, drag stabilized dart. If the butt-stock is extended Holdout changes to -5. Fired underwater 1/2D range depends on depth: at 17 feet depth 1/2D 33, at 66 feet depth 1/2D 22, at 133 feet depth 1/2D 12. Max is 1/2D ×1.5. The darts are better stabilized under water, raising Acc to 6. Use the Gun [Rifle] or Guns [Light Automatic] skill.(GURPS Special Ops gives slightly different statistics for this weapon. I based mine on data from the manufacturer. The "official" GURPS stats are very optimistic in some respects.)

 
Weapon Malf Type Damage SS Acc 1/2D Max Wt. RoF Shots ST Rcl Cost LC Holdout
SPP-1 Crit. Imp. 1d+1 10 1 27 40 2 2~ 4 10 -1 $250 3 -2
4.5×115mm (Steel Dart) [l, f]
The Russian Tznitochmash SPP-1 pistol is a  breach-loading four-barrel design. Fired underwater 1/2D range depends on depth: at 17 feet depth 1/2D 19, Max 29; at 60 feet depth 1/2D 12, Max 18; at 130 feet depth 1/2D 6, Max 9. The darts are better stabilized under water, raising Acc to 3. Use the Guns [Pistol] skill. (GURPS Special Ops gives slightly different statistics for this weapon. I based mine on data from the manufacturer. The "official" GURPS stats are very optimistic in some respects.)

 
Weapon Malf Type Damage SS Acc 1/2D Max Wt. RoF Shots ST Rcl Cost LC Holdout
HK P11 Crit. Imp. 2d 11 4 33 50 2.6 3~ 5 9 -2 $500 3 -3
9.5×117mm (Tungsten Dart) [l, f]
HK P11 The German P11 pistol fires fin stabilized 9.5×117mm darts from a cassette of five preloaded barrels. The darts are pushed by a disk that seals the barrel, preventing any gas or flashes to escape. This makes the pistol silent (-6 to hear shoots, -10 to recognize if unfamiliar with). The cassettes are not user reloadable but can be returned to Heckler and Koch for reuse (for $5 discount on new ones). A new cassette costs $25. Changing cassettes takes 4 seconds. Fired underwater 1/2D range depends on depth: at 5m depth 15m, at 20m depth 9m, at 40m depth 4m. Max is 1/2D x1.5. The darts are equally well stabilized over and under water. Use the Guns [Pistol] skill. 
Copyright © 1999 by Christoph Sticherling. GURPS is copyright © of Steve Jackson Games.
Thanks to Christoph Sticherling for allowing me to post his page on my page.