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Diving Skill

This is a new skill, based on Fitness. In order to learn this skill, a character must already have at least Swimming 1. This skill covers all kind of underwater activities (see Referee Tips below for how this affects other skills).
Possible specializations are Snorkeling, Hard-Hat and SCUBA. If you use a version of Silhouette which distinguishes between different difficulties of skills, Diving should be considered "Complex", and it needs Swimming as a prerequisite.

The different types of Diving

Snorkeling

A snorkel is a small tube that allows the diver to breathe normally by leaving one of the tube ends above the surface. They are inexpensive, easy to build or jury-rig, but cannot properly sustain human breathing beyond 40 cm. below the surface.

Hard-Hat

Also known as "Umbilical Diving". The diver wears a complete suit (see equipment) including weight boots and spherical brass helmet and receives air through a hose. Air is pumped from the surface using a special compressor.
The umbilical line usually adds a safety line and a closed-circuit communication line along with the air hose.

SCUBA

Self Contained Underwater Breathing Apparatus. The breathing needs is covered by special air tanks, usually filled with an oxygen/nitrogen or oxygen/helium mix.
Historically, 1932 is a little too early for practical use of underwater air tanks. If you really want to use them, you better justify it as a sort of prototype by a brilliant inventor.
By the same token, you should probably restrict their use somewhat. See Practical limits of Underwater Activities for details.

Practical limits of Underwater Activities

Working underwater is difficult and dangerous. Many of the dangers have been somewhat reduced thanks to scientific and technological progress, but for campaigns set in the '30s most of the technology is still in its infancy.
There are a lot of adverse factors which may affect a diver: water temperature, light (or the lack of it), the higher density of the medium in which he moves, but the main problem is the pressure.
The human body may survive at a much higher pressure than 1 atmosphere (the standard pressure on the surface). But in order to do this, its internal pressure must match that of the external medium. At just 1 meter below the surface the external pressure is already at 1.3 atmosphere (hence the limit on snorkels length).
In order to survive (and operate) underwater, humans need to breathe air at the correct pressure (2 atm. at around 10 meters deep, 5 atm. at 40 and 10 atm. at 90 m. below the surface and so on). This alone makes the use of air tanks unpractical below the 10 m. limits.
Using an umbilical rig is easier (apart from the risk of damaging the line, or get it entangled) and the safe operational limit for this is around 100 m.
Unfortunately, all is not well for the diver, even if he has an unlimited supply of air at the correct pressure. The usual oxygen-nitrogen mix we all breathe on the surface becomes a sort of intoxicating anaesthetic at higher pressure levels. The only solution was to change the mix: the best solution (albeit pretty expensive) was suggested in 1919 by an American inventor: substitute helium to nitrogen. This worked well enough, apart from the "squeaky voice" after-effect. For practical and economical reasons, most divers will use oxygen-helium-nitrogen mixes
But the worst problem for deep diving was something that no inventor could solve. Divers were aware of a lot of strange and dangerous side effects on health since the 19th century: the symptoms were similar to cramps or rheumatism, and were usually called "the bends" because just after getting back to the surface a diver could "bend down" due to acute pain. Apart from physical discomfort, this strange phenomenon could even lead to death for the diver.
The cause was discovered in 1878: nitrogen becomes liquid at high pressures, and if the body reaches the surface too quickly, the nitrogen in the system goes back to gaseous form, creating damaging bubbles everywhere.
The only way to avoid this is to resurface slowly and gradually, with frequent stops on the way up, in order to neutralize the "bubbling" effect.
The time spent on the decompression stops depends from two distinct parameters: the maximum depth you reached during the dive, and how long you remained there. As an example of this, if you spend 1 hour at 40 m. below the surface, your total decompression time would be around 27 minutes.
More specifically, you should get back to 9-10 m and wait 27 minutes before going up.
If you spend an hour at 60 m., you need 260 minutes of decompression... that is 26 minutes at 15 m, 52 at 12 m, 78 minutes at 10 m. and 104 minutes at around 6 m.
At the same depth, half an hour of work would require "only" 174 minutes of decompression, divided in three intervals (29 minutes at 12 m., 54 at 10 m and 87 at 6 m.).
Just these two crude examples (they come from a game supplement, and not from real decompression tables, btw) should convince everybody that providing actual details for a cinematic game would prove too complicated. Especially because the various factors, like the pressure in the air tanks for SCUBA, and the percentage of nitrogen and oxygen in the mix for any kind of diving, may significantly influence the outcome.
If PCs remain in the "comfort zone" (no more than 10 meters below), no decompression is really necessary. If they venture deeper, consider that the time required to avoid decompression problems is often much longer than the time spent working on whatever you need to do underwater. This is a real problem when using air tanks: a 2 hours tank would actually give 90 minutes of air at 18 meters... the "missing" 30 minutes would be used to get back to surface.
Pulp games should not bog down in technical minutiae, but if you really need them, I have some guidelines on decompression and its effects.

Equipment and Weapons

Umbilical Diving Rig

Full suit, brass helmet with windows, weight belt and boots. Weights around 40 kg. Cost: 1200 $; provides Armor:5.
Add 300 $ for the compressor. Proper maintenance and operation of the compressor would require a skilled mechanic to minimize the risk of pumping down carbon monoxide exhaust along with the required gases.

SCUBA

Historically, SCUBA activities were not very common before WWII. The stuff used to completely outfit a SCUBA diver would be either trivial (Swim Fins) or custom made (Air Tanks), so no prices are available. A reasonable "invention" would be an air tank allowing operation at maximum of 10 meters below the surface, for 2 hours. Weight would be around 3 Kg., cost around 50 $.
Any air-tank based equipment should include pressure regulators and some safety measures to make it practical.

Bang Stick

Bangstick (12 gauge) Data Dmg Notes 18+AD Requires Melee skill May be reloaded underwater. ROF: 0/2 O

The bang stick is a sort of spear, but instead of a traditional metal head, it hosts a small cylinder where a standard cartridge (usually a .12 shotgun shell) is mounted (see below for an image of the tip, note the lanyard line to secure the screw-on chamber). The shell is "fired" when the stick is thrusted with sufficient force against an object (or animal, or other diver...) I have no idea of when this weapon was invented. Cost should probably be pretty low, anyway, it's just a metal rod with a small chamber at an end and a mechanical trigger. Let's say 5$. (Length: 80 cm to 1 meter.)

Speargun

Speargun Range 5 10 20 40 0 -1 -2 -3 Data Dmg Reload Notes 10 2 turns Usually not reloaded in water. +3 Notice O

This weapon is basically equivalent to a sort of underwater crossbow. Spearguns were developed after SCUBA, for obvious reasons, so the first historical models were produced a little after the 30's. It's probably just another job for your gadgeteer characters. The model depicted here is fairly powerful for a mechanically propelled one. As such, it is a little cumbersome outside water (it is more than 1 meter long). A more advanced version (using a compressed gas to propel the spear) would have 50% more damage rating. Range would not change much, given the difficulty of properly aiming it. By the same token, even if the speargun may work outside water, do not change any stats: air is thinner, but the speargun will never be an accurate long-distance weapon, anyway. Cost would be around 10 $.

Other weapons

Use spear stats for various kind of harpoons. Knife work well, as explained in the combat section below. Other weapons are fairly less practical, unless you allow mini-torpedoes as a super-science project.

Referee Tips

The underwater environment is quite different from the one in which homo sapiens carries on his daily life. Senses and movements are equally affected, so whenever a character has to use any kind of skill underwater, apply the following rule:

While underwater, if the level of the required skill is higher than the level in Diving, always use Diving for the number of dice.

Example: Roger has Notice 3+1, Melee 1 and Diving 2. While underwater, the referee asks a roll to notice a menacing silhouette approaching him from above. Roger's player will roll 2d+1 for this. On the other hand, if Roger lives long enough to put up a fight with his knife, he will use Melee 1, as usual. Extra dice (daring dice etc.) may be applied.

When describing activities underwater, keep in mind the following parameters:

• Visibility is affected by refraction, so when looking through air (i.e. beyond a faceplate) things would look bigger and nearer than reality.
• Direct sunlight provides illumination up to a depth of 100m. Beyond this point some artificial light source is required.
• For all practical purposes, even in ideal conditions, visibility under water is no more than 75 meters. Obviously poor light, disturbed sand/mud, and other factors could further reduce it.
• Colors are also affected: reds become invisible at 6 meters, oranges and yellows may still be visible at up to 12 meters. Blue shades may still be visible at up to 30 meters.
• Thanks to the higher density of water, sounds travel well under water (both in term of speed and distance), but they scatter more, so even if loud sounds can be heard farther, their source is difficult to pinpoint with any precision.
• Remember that (at least in a Pulp World) there you may encounter some pretty dangerous inhabitants while you visit the deep sea.

Apart from the things mentioned before (and especially the all-important rule on using Diving skill as a ceiling value for physical actions) there are some extra stuff you need to know regarding combat underwater.

• As another consequence of higher density of the medium, explosives are much more effective under water. Double ranges for the primary effect (see Area value in the weapon table).
• Melee attacks are pretty ineffective, due to the greater resistance offered by water to anything moving through it. The only viable form of armed attack are those using thrusting actions, like knives, spears or harpoons. If someone insists on using a Katana underwater, apply a -2 modifier to his attacks.
• Traditional firearms are not built to be used underwater. Someone could invent/build some sort of revolver device, as a superscience project, but range will be pretty limited (divide equivalent weapon ranges by ten).
• When fighting someone using a diving rig, allow a -2 modifier for attacks targeting the breathing apparatus (this could be the mouthpiece or mask for a SCUBA, or the umbilical line for a hard-hat diver). Success, regardless of the actual MOS, would probably force the enemy to flee or drown him outright.
  Please do not let players abuse this. Grabbing a mask and yanking it away would be a reasonable -2 unarmed attack against a SCUBA diver. Trying the same trick to tear away the umbilical hose of a hard-hat diver would be futile, unless you have inhuman strength. On the other hand, trying to sever it with a knife could work... but hoping to sever it with a well placed spear from a distance would be practically impossible.

Bibliography

The Undersea Environment

by J. Andrew Keith, published by Gamelords Ltd. in 1983
An old Traveller supplement, including lots of hard data about diving. Hard to find, but gives complete statistics on most aspects of underwater activities.

GURPS Atlantis

by Phil Masters, published by Steve Jackson Games in 2001
Less hard data, but still quite interesting, and with a lot of info on Atlantis, a powerful myth which could prove useful for a Pulp campaign.