I'm no diver, but 144m is pretty deep. Early WWII subs couldn't even make 160m, much less a diver in a wetsuit. At 144m that's already about 190psi (or 131 kPa).

144m isn't for the average civilian, standard PADI qualified divers are qualified to dive till 18 meters, i believe civilians don't go any deeper than 60meters, not sure abaut military though

I am a padi open water diver and i can't go deeper than 25m. I believe some go as far as 50m but only with special training and special gas. Anyway, would be good if some mission designs could incorporate a element of real diving to make things more challenging.

When you use rebreather in military missions, they use pure oxygen what become dangerous if you go any further below than about 10 meters.

If you use open circuit scuba gears (like most hobby divers use!) you will dive no more than 30 meters below surface. If you go deeper than that you will get nitrogen narcosis.
If you are military diver, you are trained to dive under 50 meter below for short period of time.

After that you will use differend kind of gasses to go further below.

oxygen rebreathers are currently limited to a depth of 6 meters (20 ft)

There are many types of re-breathers some can go alot deeper then others but around 50m is about the max (besides they wouldn't need to go that deep on a mission)For example extreme cave divers use re-breathers to go around 50m

With rebreathers it is possible to dive up to 200 meters and more, but this is not the common case. Normally, like it is already said, you stay above 50 meters, but keep in mind that we are out of the hobby-area and the scenario is playing in the future!

A diver can get to ~300/400Meter with a technical diver license.. so dont worry about diving is too deep.. BIS should just make oxygen tanks and different mixtures..

http://wiki.answers.com/Q/What_is_the_maximum_depth_a_human_can_dive_to

Re-Breather Use
The options for modern exploration are most commonly open circuit scuba and re-breather. Diving is limited by the correct mixture of breathable gases. On open circuit "classic" scuba the gas must be mixed ahead of time, while on re-breathers a diver always has the right mix of gas for the depth. Australian diver David Shaw successfully used a modified recreational re-breather to reach a depth of 888 ft (270 m) in fresh water in 2004. (Shaw died on an attempt to recover a fellow diver's body in 2005.)

Nitrox enables deep long dives.

1. Longer Bottom Times: Recreational nitrox (21 - 40% oxygen) contains a lower percentage of nitrogen than air. The reduced percentage of nitrogen in recreational nitrox allows divers to extend their dive time.

(National Oceanographic and Atmospheric Association) no-decompression dive tables, a diver using Nitrox 36 (or NOAA Nitrox II) may stay up to 50 minutes at 90 feet of sea water, while a diver using air may only stay a maximum of 30 minutes at this depth.

I'm not going to vote up or down on this, but i can live with what already is existing in alpha for diving depth. Remember that this game is based in the future, so there is room for a little freedom in this department. If you need to pretend in your own mind that you are using a type of gas, to feel comfortable, then go for it. Either way this issue should not effect many, but for simulation purposes, it is a good thing to discuss realities and i hope whatever they do makes sense for what they are trying to portray, but i'm not an experienced diver, so my opinion does not count, but i just wanted to express my unbiased opinion about this.

For TACTICAL reasons I vote UP. Because - as allready sad -

1. there is either a very light and small diving gear with pure Oxygen = 6m for hours / but only minutes in deeps > 20m !!!

2. the are of course also rebreathers with mixed gases. BUT this gears a much bigger and heavier. = this should affect the Inventory!

So it depends from the MISSION, wether a Diver should choose the small one or the bigger (Tornister).

Today (1) is mostly used to get (only) ashore. (2) is common for finding and disarming mines - because the are often droped in deeper water...

I don't think they should put a floor to how deep you should go (i.e. prevent you from swimming deeper than you should), but set a depth that you start taking damage at depending on the type of diving gear you are using. Actually if you used no gear at all, you could dive down to 60m and not get hurt. However your stay wouldn't be all that long.

There are people (Freediver) the can go down to 120m and more with only taking one breath.

So it is possible to dive 60m and not get hurt. IF You don't stay there long.

Other question is, how many soldiers would be freedivers with years of training?

I would set 20-30m as a limit for diving with NO equipment. Beyond this limit I would reduce the health dramaticaly over a short time.

But of course ESCAPES from Submarines are a different thing. There are known successfull Escapes without any gear from deeps about 60m....

In reality no soldier with all his equipment would dive deeper then 3-5m at all. I'm pretty sure about this. :-) And he would not stay longer then 1-2min.

A trained SEAL may beaten this numbers ... but not so much with a land combat payload.

Adding realistic oxygen/gas mixture usage calculations (for free diving and diving with rebreather) would solve this. Like fuel for cars...
The deeper you dive the more oxygen you use, the more you move the more you use.

Your body does not use more oxygen when You dive deeper. Oxygen consumtion depends not from the diving deep, only from metabolism = how fast You move.

Due to this fundamental behavoir a REbreather works very efficient. Because in this CLOSED LOOP System its only the tiny amount of oxygen what is replaced continually.

And in a pure 100% Oxygen Rebreather there is no father Diluent gas, that makes this gear so fantastic easy. But the major problem is the toxity of pure Oxygen under higher PARTIAL Pressures.

A solution is to use an so called Diluent gas - as a thinner. This gas has to be nontoxic and shall do nothing to the organism.

The best known Diluent/Oxygen mixture is NYTROX. Our athmosphere is a special mixture of Nitrox. (21/78) This works well down to deeps of aprox. 40-60m. For shallower deeps You would increase the amount of Oxygen... If You dive really deep with Nitrox, You run either into trouble with too high Oxygen Partial Pressure (toxic!) or to high Nitrogen Partial Pressure (narcotic!)

So this is the area for other Diluents, like Helium or Hydrogen...But the become also problematic under extrem high partial pressure.

So the basic Issue for diving in a wide spreaded area of depths is to control the partial pressure (= the percentage in the mixture) of the Oxygen over all depths. Therefore it is essential to have Oxygen Sensors and Control Valves. This makes a Rebreather for higher depths simply more complex. Bigger. Heavier.

But theoretically You will have the same dive time with the same Oxygen supply - regardless of the depth.

But of Course You will have the problem of becoming free of the dissolved Diluent gas - depending of the time You was under higher partial pressure. So a Decompression procedure becomes mandatory.

For the Game Play:

I would say at least there should be a time penalty to leave the water after deep dives. And - as mentioned before - deep diving gear should be bulkier and demand more inventory space. Diving deeper with a "normal" gear should result in an injury countdown.