Realistic Equivalents (TFTD)

• Pistol-type weapons
  • AAI underwater revolver. http://en.wikipedia.org/wiki/AAI_underwater_revolver
  • SPP-1 underwater pistol. http://en.wikipedia.org/wiki/SPP-1_underwater_pistol. Small calibre ammunition designed for underwater use. More effective than spearguns. Inaccurate above water. 4 shot capacity (4 single shot barrels).
  • Heckler & Koch P11 Underwater Pistol http://en.wikipedia.org/wiki/Heckler_%26_Koch_P11_Underwater_Pistol This is the actual Dart Gun! 5 shot / 5 barrel. 10m-15m range underwater, 30m on land. Fires 10cm darts. Not reloadable in the field.
• Jet Harpoon
  • РПБ-1М pneumatic 'military spec' speargun. 5m range, single shot, not terribly effective! http://forums.deeperblue.com/pneumatic-spearguns/94639-russian-1-pneumatic-speargun.html
• Rifle-type weapons
  • APS Assault Rifle http://en.wikipedia.org/wiki/APS_underwater_assault_rifle. Older underwater assault rifle. More effective than spearguns. Effective underwater range 11m-30m (dependent on depth). Difficult to use, power similar to a normal pistol, less effective than normal firearms above water - 50m range, limited lifespan. 26 round magazine. (Not clear if auto fire works underwater).
  • ADS Assault Rifle http://en.wikipedia.org/wiki/ADS_amphibious_rifle. http://world.guns.ru/assault/rus/ads-dvuhsredny-e.html. New selective fire underwater assault rifle based on the A-91M. 18m-25m effective range underwater (dependent on depth). Uses a very elongated, pointed bullet. Genuinely dual-use (water/land). Can fire normal ammunition very effectively above the water, uses standard magazines, and standard ammunition above-water. 30 round magazine. Grenade launcher and accessory capability. (Not clear if auto fire and the grenade launcher work underwater).
  • PNW MEA underwater rifle ammunition in 7.62x51mm NATO. Standard NATO bullet travels 2 feet underwater, this has an effective range of 30m. There is also a variant of the ammunition with very high antipersonnel damage. http://www.defensereview.com/dsg-technologypnw-arms-multi-environment-ammunition-mea-solid-copper-general-purpose-supercavitating-gps-and-tungsten-penetrator-tipped-dual-core-supercavitating-dcs-armor-piercingarmor-penetr/
• Grenades
  • Mk 40 Mod 0/1. Anti personnel depth charge. http://en.wikipedia.org/wiki/United_States_hand_grenades#Mk_40_Mod_0.2F1
  • MAXAM EXPAL GAB Underwater Grenade. For anti-diver use. http://www.maxam.net/en/expal/products/weapons_systems/gab_underwater_granade [sic]
  • E-105 fragmentation grenade. http://www.pmulcahy.com/hand_grenades/british_hg.htm
  • M67 grenade (possibly just for surface use by frogmen?) http://en.wikipedia.org/wiki/M67_grenade
  • M14 incendiary thermite grenade. A demolition type of grenade for underwater use. http://en.wikipedia.org/wiki/United_States_hand_grenades#M14
• Dye/Smoke Grenades
  • Seems to be a consensus that smoke grenades would not work
  • Can't find anything like a dye grenade...
• Underwater Demolition Charges
  • Many types and models exist...
• Gas Cannon / Hydro Jet Cannon
  • Arsenal RLV-AD anti-diver 40mm grenade round. Not clear if it can be fired under water, or needs to be fired into water. http://www.defensereview.com/arsenal-rlv-ad-anti-diver-underwatersub-aqua-and-rlv-tb-thermobaric-fuel-air-40mm-grenade-rounds-for-military-special-operations-forces-sof-and-special-warfare-specwar-applications/
  • MRG-1 MULTIBARREL ROCKET GRENADE LAUNCHER with RG-55M-1 rocket grenade and the UG-45 universal grenade to engage frogmen. (Link broken)